Easier to get SE/30 than to try and upgrade Mac Plus.  Mac Plus is limited to max 4MB, no internal hard drive without serious hack, and the tiny keyboard isn't too comfortable compared to Extended Keyboard II. Plus you're also limited with choice of mouse for Plus vs SE/30.   SE/30 can have really huge memory upgrade although anything over 8MB is probably overkill.  

For all-in-one color, something like LC or Performa 550 or 575, they support 640x480 which are required minimum for some games.  Color Classic and II as well as Performa 275 have smaller display and may have problem with a few color games.