I would say it depends entirely on what the printer actually is.
Machines like the bnc3d sigma and leapfrog bolt - with dual independant heads, definitely a good idea. If I could afford one I'd buy one asap.
Or the machines with the 2 feeds into one nozzle setups. Not quite as versatile, but still pretty good.

Things like my replicator clones - not so much.
With a conventional extruder you need a serious dribble wall, or the filaments get mixed quite a lot.

Software is very important. I have never managed to get simplify3d to do effective dual extrusion, still end up using an old version of makerware.

I'm not planning on any new dual extruders in the future.

on another note - you guys going to be at tct this year ?