hmm, bang for buck? just some fast ram. double your speed for 30£$E...
i managed to get my bliz030 for £45 which was a steal. especially since i've seen some going recently for around £100+!
an 030 is fine for everyday stuff and games, and will be very stable, plus run off a standard PSU.
But start doodling around with photogenics, imageFX, and ray tracing, you'll be wanting more power.
something along the lines of an 040 or 060. once you've booted with an 060, an 030 seems like such a step backwards, you'll be wondering where to shovel the cole in to get it going.
memory. well, 4Mb is good enough for odd bits and pieces, basic stuff, have an IP stack running in the background while having dpaint open and a music player.
8Mb is fine, but you'll find your limits fairly quick.
but then, having said that, great things have been done on machines with less...
16Mb to 32Mb is great. even though not much "classic" software really needs more than that, you always find a use for what you have available. :-D
if i was given the choice between a 4Mb 040, and an 8Mb 030, and no chance of an upgrade, i'd go with the more memory. but i can't think of any 040 boards that are that limited. even the PPS040 card for the A500 had 8Mb on board.