I'm not saying that a strong contango in VIX futures won't help XXV's returns--it definitely still will. What I'm saying is that I believe XXV and VXX will both fluctuate around an ever-decreasing center of mass, due to rebalancing and fees, that will cause it to be a poor investment choice long term, like many other ETFs/ETNs. Again, to re-iterate, this is aside from roll yield considerations. Basically, over time, if you would like to buy XXV, the better choice will be to short VXX.
See my earlier post Uptrending Equity: Volatility arb to see how I'm profiting from the presently large VIX contango.