I have an svg image made in Inkscape with about five raster images embedded in it. Each of these images is used many times (up to 72). Each of these images is small (<1MB), but judging from the file size (>80MB), the images are not reused but embedded over and over again. Can Inkscape somehow minimize it and have each unique raster embedded only once?
Yes, it can.
Embed the original image once and for each other instance of that image use a clone (Edit → Clone → Create Clone) and not a duplicate of the original image.