With the Yankees acquiring Pineda, there's even more incentive for the Sox to go with their current staff. By staying under the luxury tax this year, they can be sure they can get a top-tier pitcher next year with the Yanks out of the running.
That is, of course, if they manage to stay under the luxury tax. By my calculations, using the link you posted yesterday, they'll be around 172 million for next season (I projected my arb numbers a bit more conservatively), meaning they have enough room to play around with a couple of the re-treads.
Only one of the re-treads needs to work out for the sox to have a convincing rotation next season.
However, the possibility still exists that they come out holding the short end of the stick in arb, go over the luxury tax, and sign Oswalt anyway because they did.
This situation can play itself out a number of ways, and only one (going over the luxury tax without signing the pitcher) could be considered as negative.