I still have my MOD50 head and five modules, but the fact that I can't get an OD/dist pedal to sound good through the T/D or BMAN modules is kind of a dealbreaker.
My other amps are a Peavey JSX combo, a Peavey XXX head (original version) and a Fender Super Reverb head/212 + dirt pedals (not exactly top shelf stuff, but they work for me).
I'm leaning toward slimming it down to just the JSX and Super Reverb. The JSX takes pedals much better than my MOD50 does (on the T/D or BMAN modules), and the XXX is way too bright, even with JJ 12AX7s.
I may change my mind after NAMM - having only two modules at a time is really limiting. A SYN-2 would put me back at the M4 level.