..I guess its not possible to remove all off-topic posts from this thread?
Right, on-topic, I just wanted to say that I had an unexpanded a1200 and a4000 and in the end I choose the a1200 for my 'upgrade path', since thats the only machine that can scale right down to basic 2MB 020 cpu by the press of a button. apart from that, a a towered a1200 offers a lot more space than a desktop a4000.
As far as upgrades go, the mentioned ACA 030 is great, as is a second-hand blizzard 1230 or even 1260 (although for that money, please consider the blizzardppc instead). You' ve got to understand that you're stuck with AGA, which is very slow on higher resolutions. I would recommend an indivision too and I bet you have a 3.5" harddrive in there already.
good luck expanding and enjoying!