I think some of the fun is very definitely in the stamping and punching etc - I still feel it's a bit like magic when I press an inked stamp onto paper and a picture comes out! I can see having 30 people make the same thing would be impractical though so I'm thinking out loud here.
- Maybe you could come up with a simple basic layout and cut any panels that need cutting (do some extras for the inevitable accidents) ahead of time. Everybody will work towards that basic design but their actual end product will depend which table they sit at.
- Have different stamps and ink on each of the different tables so people can stamp on the main panel of their card for themselves - you could even have a table for masculine, a floral, a kid's set etc. Try to pick sets that don't need colouring in since that's a skill in itself and can take a lot of practice to get right (not to mention the extra tools you'd need to supply!). Have some samples to show that are based on the layout and the stamp sets you've chosen so people have something to copy.
- Do a little demonstration of how to ink a stamp, line it up and stamp it. Put some scratch paper on the tables so anybody who has never stamped before can have a practice before they do it for real.
- Maybe have a selection of punched shapes and perhaps embellies like brads or bling that don't need any special tools to apply them for each table - depends on your layout I guess.