Xpantastic!

Ok, this is not really a "vs." but more of a "worth the upgrade?" question.  I am thrilled with my xpander, but have the opportunity to buy an M12 locally.  Obviously, double the voices of the xpander, but also (in my mind) double the potential for voice failure/problems.  However, I am still tempted as the price is less than what they are currently going for.

Although it would be nice to have more voices for the sake of having more voices, I am wondering if others found the M12 to be more gratifying in any other way.  I currently treat the xpander more as a single polysynth rather than a multitimbral/monosynths, so I would imagine having the extra voices would be useful.  I also understand the m12 can double voices too... 

Any advocates for the upgrade or would this be a gratuitous purchase?