I don't think you need to show entire spreads. I think too often portfolios start to focus on the minutia when really its the global design sense that is being investigated. Few will really care what that last third of the left side in a spread looks like if they see the right side and 2/3rds of the left side.. or what the back cover of a piece looks like if they see the front cover. What is being most often examined is a sense of size, balance, space, proximity, color, etc. Showing these aspects is far more important to me than showing what that top right corner of a spread looks like. I try and remember that portfolio reviewers, for the most part, are conceptual people. They can extrapolate some things given only some information. And if they aren't conceptual in nature, no amount of visible detail is going to overcome that to a degree.
Form vs function :)
I look at the portfolio as a "tease". I want others to want to see more. So, I purposefully create portfolio images which show the overall design but not necessarily everything. Remember the function... to get you a call back or to have the viewer reach out to you. So, leaving them wanting more is a good plan to help facilitate that.
I have never shown a full spread or piece in a portfolio image.
Unfortunately, it is impossible to convey things like paper texture or even relative size sometimes digitally. You simply have to let that go much of the time. I am not a fan of photograph of people holding pieces or of the flat "magazine spread mock-up" 3D templates out there. (I detest that gutter curve which any human who has ever read a book knows is there, you don't need to show it.)
While these "canned" templates can be helpful to some. There are really small 3D apps out there for free or with a minimal cost and learning curve which will allow you to create your own 3D scene with merely flat images or even PDFs of a piece. So, this is what I use.. a 3D app and I create my own scenes. And I'm NOT a 3D designer. And the great thing about this is that the actual content images can be swapped in the 3D app.. so you can configure one set up, then merely swap cover/page images and have a new set up. (And then shuffle pieces around for a different "stack" to not appear as the same setup).
I tend to set things up in a per-client manner to show overall brand continuity across a range of different pieces. This does help convey the relative size of pieces. Stock texture is still a non-starter.
This gives the viewer the opportunity to see the general design aesthetic across multiple pieces but doesn't focus on any specific aspect of any one thing.
I do realize the bulk of possible pieces to show can be a detriment with this manner of display. Not everyone or every client will have multiple various pieces you can use in a portfolio.
If dealing with a single piece I do the same thing essentially.... show the imperative aspects, but leave some to the imagination.....
Cover with a spread...
.. just a spread....
At times... A spread with additional pages.
(Page content pulled from Google Image Search labeled with right to reuse.)
Again enough is shown to hopefully entice the viewer to reach out to see more.
For the display of spreads I present them clearly with minimal distortion or curve, but still with some aesthetic sense nonetheless.... I, personally, have never seen the benefit to the overly perspective view or the pseudo "lying on a table". That, to me, assumes the viewer doesn't understand the concept of a "book" or "magazine". In the images above, the angle of the sides is enough to convey "spread".
All that is required is a PDF or image of the page for use in a 3D app. So typically you can merely yank a single page out of an existing PDF and use that.
Then, if someone does reach out and happens to ask to see more of a project, I have web page on my site that merely contains flat cover images and a link to PDFs. I can forward a link to an individual PDF or forward a link the entire page of PDFs. Then the viewer can download and flip through the (locked) PDF like anything else.
One thing I never do is have multiple portfolio images showing spread A, then spread B, then spread C, then spread D, etc, all from a single piece. At MOST I'll show 2 spreads of something and I try to elegantly show both spreads in one image. A portfolio gets dramatically more boring exponentially for every "spread image" you show from a single piece. 2 spreads should be sufficient for any piece. Merely select the 2 spreads that show off as much good design as possible. Again, you don't need to show everything related to a piece. A portfolio is not indented to be a complete and accurate "library of past work". Its purpose is a "few examples".
All this is much different in person.
In person, I have a collection of a few of these "group" or "gang" images in my hard copy portfolio, then I have a few printed samples in my bag. If asked more in-depth questions about a project I can whip out the printed sample to allow the other person to flip through it.
I naturally don't carry around a 60lb bag containing samples of everything shown in the portfolio. I simply carry a few of the different pieces which I feel may warrant more questions or have specific areas I want to show off if an interest is piqued. This does allow my to explain more about stock and the "feel" of a piece in one's hands.
For "drop offs"
I hate these.. but they exist.
The best impression I've seen made is a photo book. I think of the portfolio images as photographs and I need a "wedding album" or something of that nature.
Years ago this was a chore, in today's age it's an easy thing overall with really minimal costs. There are many "photography" services that can create "albums" and you are free to design and customize to your liking. With some searching, you can find services offering albums that don't appear like every other album out there or which will create a custom sized album. Basically you look for a "photo book service" as if you were a photographer. You have to get past and ignore all the "fluffy" wedding and family covers they use to try and sell to grandma.... and look at the specifications of the album and what you can and can't alter or customize. Basically.. ignore the sugary covers and example images and find the "bones" you want to use.
(The link is not an endorsement of that service. I've never used it. Link is provided merely as an example.)
You simply have high quality images of your portfolio pieces -- whether that means you invest in some product photography with a professional photographer, or you use a 3D app to make good product images doesn't matter. The actual portfolio images are merely treated as photographs.
So.. you follow everything I've posted above and end up at some high-quality photographs to show off.....
You then get an actual book made using these "photographs". Perfect bound, glossy hard cover, etc. Dropping of an 8x10" book will really make one standout in a stack much of the time. It shows a level of professionalism and attention to presentation detail many students struggle with.
Believe me, the impression this makes on reviewers is light years ahead of someone dropping off an old-school, zip up, "portfolio bag" with single artboards inside it. And you are free to set up the pages any way you wish since it's all merely seen as "photographs". You can place explanation copy if desired, or show full pages, etc.
Of course, if others have dropped off a "book" then it's a matter of whose book is better :)
In my days of job interviews I had 2 portfolios.... one for drop offs with a some cursory text explaining what the project was or a specific hurdle I had to overcome, since I wasn't going to be there to explain. And then a portfolio with no explanation copy whatsoever. So that I could speak about the project(s) and reviewers were forced to ask if interested. Then years later a 3rd portfolio online which is somewhere in between.
Disclaimer: It's been many years since I've had a portfolio showing in person. Everything has been digital for a decade or more.