I think the only real con is your limited color space. And that isn't necessarily a huge con...
Some great designers have embraced the photocopier.
One that comes to mind is Art Chantry who, IMHO, is just as responsible for the Seattle Grunge scene as Nirvana was:
Granted, that's a particular aesthetic that may not apply to your org's needs. But there's also lots of great b/w poster design out there. Paula Scher has done some really wonderful poster work in limited color pallets:
Photocopiers today are quite good, so note that I don't think your average person is going to particular notice the device that printed the poster. So your issue isn't so much the photocopier as it is the fact that you are working with a limited color pallet. Some suggestions to explore:
- colored paper.
- negative space. Really play with the toner as a medium.
- tiled posters printed across multiple sheets...perhaps multiple colored sheets.
- consider color copiers (fairly affordable these days)
- If the quantities are low, consider adding color via other methods (rubber stamps, spray painted stencils, etc.)
Beyond the copier, if press runs aren't crazy large, maybe explore screen printing.
Bottom line is don't consider the photocopier a limitation, but rather embrace it as a challenge. The best design, IMHO, comes out of a well defined scope. It forces you to push the boundaries more than you may realize.