Again: why? The Pirates semi-successfully recast Vogelsong as a not-completely-horrible reliever last year. If I'm them, I congratulate myself on a job well done and never again try to add another level to Vogelsong's house of cards.
Vogelsong has a 6.74 career ERA as a starter. He has a 4.23 ERA as a reliever. A 4.23 ERA isn't very good for a reliever, but the Bucs should be able to live with it as long as he's cheap. His strikeout and walk numbers are about equally bad as a starter and as a reliever. The only major difference between Vogelsong as starter and as reliever is that he's given up a lot fewer homers in his time as a reliever. Maybe he's kept the ball down a bit better, but the point is that it's not as if he's made some major change in his approach that would lead one to think that another trip through the rotation would be different. And he's not young - he'll be 29 in the middle of the season. He's a mediocre reliever at this point. Anyone who had to watch Vogelsong start in 2004 should be grateful for that. My advice to the Pirates: Don't fix what might look a little bit crappy but nonetheless isn't broken, and might really become broken if you tried to fix it.