RIM's market cap is $15 billion, so buying them just for the patents would be like burning $100 bills. As a comparison, Nortel's 6000 patents are apparently getting sold for less than one billion. Does RIM have a portfolio anywhere near that size or quality?
To be fair, buying Nokia will be much cheaper. Phase one of the plan is complete and now phase 2 is under way. In a few years, Nokia will be so dependent on Microsoft an acquisition will be unavoidable.
OTOH, RIM's market cap won't last long. Eventually, they will be a bargain.
Now that Microsoft has no longer the antitrust ghost to haunt them, they are free to do a lot of nasty things.