Just think of the A1200 as being an A600 with clockport, more available accelerators (although I believe Jens just released a cheap-ish accelerator or the A600), more powerful/more memory in stock form, AGA of course, numeric keypad, etc.
It's obviusly "better" than the A600 & if you can afford one, I think everyone here would suggest you buy one
That being said, if you don't want AGA & are just interested in playig "classic" Amiga games, maybe you don't actually need an A1200? However, some would classify "need" & "want" as being the same thing...LOL
Anyway, grab an A1200 & have the best of both worlds I say
By the way, you CAN use 3.1 on your A600 if you install the correct ROM
PZ.