VGcharts now has December numbers for the PSP version. It looks like the game sold 72,000 copies in December, a little less than 2x the November numbers. The game is now at 124,250 copies sold. I really don't know how PSP games continue to sell overtime, but I'm leaning towards overvalued on this one.
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http://www.vgcharts.org/usagamemh.php?name=Marvel%3A+Ultimate+Alliance