I bought the modular first, but then I checked out the demos. I played one note on the CS80V and thought `I've got to get one of these.'
I explored the demo a lot further and decided I definitely would, and I also liked the 2600V.
There was an offer on the Vintage collection, including all four synths, so buying that was cheaper than buying the CC80 and the 2600 separately. So I gave the extra MMV to a musician who could do something worthwhile with it, and I now had the MiniMg as well, which I hadn't originally intended to buy.
But when I explored the Mini I found it had something extra, in addition to what the MMV could do - and also something extra over my hardware Mg Voyager.
Of course it depends on what you need. My setup works for me and may not be what someone else may need. But I'm very glad circumstances led me to get the Mini as well. In fact the only thing I might do differently with hindsight would be the purchase of the `real' Mg. I'm very pleased with it, but if I was buying now I might go for the Creamware MiniMax instead. I know two former MiniMg players who've done that, and both are very pleased with it. It's polyphonic and it's cheaper than a Mg Voyager.
I think I've partly answered your second question. The Mini has a different character from the MMV, despite of course being more limited. In addition I like the arpeggiator, which is far more interactive than the MMV's sequencer in ways that are useful to me.
BTW my music download page includes pieces done entirely with the MMV and the 2600V. I'd like to add MiniMgV and CS80V pieces as well, and a Voyager track at some point:
www.myths-and-legends.org/andrew/