There's not much that can go wrong with an A500 motherboard besides the chips (which you're going to need for the new motherboard) or the sockets (which are easy to replace).
Why buy a whole new motherboard to populate it with 25 year old chips that could fail at any minute?
Maybe because it's a cool thing to do with the hobby. Why not WinUAE. Why not throw you into a sausage grinder? Both provide the same entertainment value.
The side expansion connector on an A500 is pretty much ZII. If you want to use a ZII card on a A500, only a simple adapter is required. You're not going to fit any standard ZII card inside an A500 and still be able to close the case.
There's a right-angle Z2 adapter shown up the thread you flipper armed mong.