One thing about thinning down your collection and keeping the A2000 is that the A2000's have always had a good track record for longevity. I wouldn't be surprised if there are more A2000s still running than any other big box Amigas. So if you are going to have less Amigas then the A2000 seems a good choice.
well, that's quite obvious given their size (so the PCB tracks are wider, cooling etc..). also, iirc they are two layered PCB compared to 4layers in a4000 (or something like that).
still, leaked battery seems to influence them most. because it is near the CPU. I never had such problems with other Amigas. apart from that, they are very sturdy.
but if one has more Amigas, A2000 takes most space.. (except maybe A4000T or A3000T).