Some MP130s run Newton OS 2.0 (the eMate/2000/2100s run 2.1) which is pretty much the same - except the later models running 2.1 can run Newtworks, support greyscale and sound manager. For older model Newtons running OS 1.x and 1.3, there isn't a lot of software that works on these and I'd put them down as more a curiosity than being able to actually do much in today's world. So as a minimum consider a MP130 with NOS 2.0 to "do stuff"

I don't know about IMAP syncing, but another plus of the 2000/2100 is dual PCMCIA slots, so you can run a network or wireless card in one slot, and cheap PCMCIA --> CF card adapter to haul up on software. You only have one PCMCIA slot on older models. And yes the performance; as mentioned to "do stuff" it really is a difference between night and day trying to do things on a 2x00 StrongARM equipped PDA vs. the older ARM models. A PDA should do things simply and responsively, and this just doesn't happen on older Newtons.

JB