If just must upgrade, then go for the A1200 instead and keep the A2000 in it's current state when you want to mess with oldschool Amiga.
At least that's what I did; I have my A500 with GVP card and Kickstart 1.3 and other expansions, when nostalgia kicks in, and various upgraded Amigas with more horsepower when I need to do anything useful. Yes, WinUAE would give me even more horsepower, but it's just not the same :-)