Yes, it's worth the extra cash. I've found it to have better mids, comfort and a better soundstage.
Some say the V6 has great mids, but my ears hear a slight recession somewhere. Also, why on earth do I find the V6 bass heavy, but the M50's bass was a little bit better? Maybe my ears are playing tricks on me! I think I remember the M50 having less mid-bass as well.
M50 is a lot less portable though. Strangely enough I've found the 7506 sounds different than the V6. Maybe my ears just changed. Who knows.
M50 is considered bass heavy it seems, so if you don't like that, I'd avoid them. My pair was, but the white box versions are said to be more balanced perhaps?