I have a poly 800, and an alpha juno 2.
I like the poly 800 for its weirdness and because of the fact that it does have one filter per voice. This makes it a unique piece. Sure it is a limitation, but people still play monos and that is a limitation as well. So being paraphonic isn't a negative thing, it is just to be played differently.
That being said, it you want a synth that will cover more sonic range, get the roland. If you want a unique piece that can do some very interesting things (6 part envelopes, easy mods), get the poly. There are many sounds made by the poly 800 that i have tried to recreate on other synths, and haven't been able to.
I would buy the poly again if mine broke.