The weekend/non-holiday rate is $89, so 8 of those are needed to pay for an MVP. Canyon will be open to April 22, so next year's MVP is only good after that. With this year's snowpack it looks to be similar to 2007. They will probably make it to Memorial Day but it will be a close call and this May I would not look at Mammoth as a weekend ski destination but maybe a day of skiing on a trip doing other activities, hiking etc.
I've had MVP since spring 2005 and this will probably be the 3rd season I don't hit the breakeven. But on the good years I exceed it by a lot, topped by 25 days in 2010-11. If 10 days is the max you'll get it's a marginal call to put up the $ now. There are always unforeseen contingencies that can reduce your projected ski days. If you think you'll get 15+ if it's a good year then it's likely worth it.
Season length: 21 months, Nov. 29, 2010 - July 2, 2012
Days in one year: 80 from Nov. 29, 2010 - Nov. 17, 2011
Season vertical: 1,318K in 2010-11
Season powder: 291K in 2011-12