Considering the Vikings viewed Jared Allen so highly that they nearly parted with two first round draft picks, I can see they being just as agressive for a franchise QB too.
I think they learned that they are better off negotiating a better deal than parting with the top picks in following years. Last year, they traded their 17th, 73rd, 82nd and swapped sixth round picks. I really don't see the the Pats getting two first round picks for Cassel (even though I would love to see it). Most likely, and without any disappointment from me, they will part with their first round pick and some combination of 2nd and 3rd round picks from either this year or next. Maybe they feel confident and are thinking next years first round pick will be #32 and shoot for the moon too.