Well... As Hobo said, it makes a difference if you need to drive it regularly.
But, there's little hope of simply "repairing" much of it without replacing a lot of it. There are kits to "repair" the dash cracks, but teh repair is always obvious afterward. You could cover it with a dash mat, but I'm not sure how tacky you might think that looks. Seats can be recovered at any decent upholstery shop. Carpet is too inexpensive to try to repair, and will make the biggest difference in the way it looks, just get a kit from JC Whitney. Same for headliners.
You might also be able to match up the factory seals with JC Whitney, or do some Google searches online for actual suppliers of older AMC restoration rubber. Hemmings Motor News magazine is also a likely source. And here:
Unfortunately, all of it requires some disassembly of the car. If you have to drive it, start gathering parts until you have enough to do a good chunk on a weekend. It's best however, to not have to drive the car while you work on it, if at all possible.