If I only had the motherboard and little money ~35$ : I would find a thin metal case (i.e: an recycled audio one = 0$, or from a server) or make a wooden one (recycled 0$), stick a small atx psu recycled from old servers (5$), two disk drives (30$), and I would be able to play games, use deluxe paint and protracker; on the thinnest amiga 2000 ever, I would call it "Amiga 2000 AIR".
If you want to go the highend route I can only recommend getting a 4000. At least you can play aga games and demos and there are some that can benefit from the 060. The only trouble is that they are hard to find without leaked batteries, they also have the bad caps problems. Whereas I got two amiga 2000 and removing the battery was easy and there was no damage at all. Amiga 2000 are simply more solid.
I had a friend who had an Amiga 2000, with 060, lots of ram, scsi drives, picasso II, it was fine for DTP, or photo editing, small 3D projects under lightwave or imagine, but we couldn't play avi or quicktime well : poor framerate. But it was in 1998 and now nobody cares about avi or quicktime and you find small divx players that can read from a sd card for 30 euros
Three years ago I could have bought a 040 amiga 2000 in a huge tower (the original 2000 chassis was fitted inside) with picasso IV and scsi for only 140 euros but I didn't see the point in having an enormous heavy amiga workstation when I had a pc which could do much more under winuae. Unless you're into video toaster, I think it's the only good reason you would want such a config, the rest is just nostalgia.
[edit: well after some more thinking, having myself two bare 2000's, I can see why one would like to upgrade a 2000, if you like the big case or if you like starting from something really bare and upgrade it, plus you could learn a lot that way, although the result would not be the most powerful, the cheaper, or the easier to do, it could be cool in its own way. After all , that's why we use amigas don't we ?]
