I think you would get better value trading Lowell. Im not saying a better player, but rather the value of holding onto Rolen and getting a SP for Lowell will be more than holding onto Lowell and getting a SP for Rolen.
Just my .02.
You have fine pitching though. 4 Closers is a luxury. Schmidt and Oswalt will compare with any 2 SP in your league.
If this were my team, I would look to make 2 for 1 deals hoping to upgrade my C or 1B with another power hitter. Maybe OF and to a lesser extent SP too. Webb is a decent #3, and Peavy a solid 4, but wouldnt it be nice to get a better #3 and make Webb an incredible #4 and Peavy a great #5? My point is you dont need to shoot for the moon in getting a solid SP. Maybe target a Bartolo Colon or Josh Beckett - pitchers in that range.
Ceck out my autodraft team is you get a sec.