Sure, if the rotation hits a major injury, he'd be much needed. But, until that happens, he is a luxury not a necessity and it might be silly to go out of budget to sign a luxury and hamstring your ability to obtain a need at the trade deadline....especially when that luxury is a bit of a gamble in itself.
This is the key for me. If it was almost any other injury he went thru last year, I'd be inclined to say that since he was really good at the end of the year then his problems are over.
But the injury was a sore lower back. For pitchers, that region is always a concern, ESPECIALLY with guys Oswalt's size. He generates most of his power from the legs and the lower back and the back gets all the strain. The only treatment for this is rest, and the older you are the more severe the inflammation becomes and the longer rest periods are needed. His injury problems are only going to get worse IMO.
So I think that spending the 10 on him actually makes the team worse by the end of the year, especially if you have to move a JW to make it work, because I think Oswalt will need the backup for injury, not that he'd be the one to help be a backup.
Not to toot my own horn... but... "toot"