Borowski is almost worthless since he may lose his job any day. Since your only real weakness is at closer, I would target them specifically in your trades. It's worth your while to research who is closing for which team and go for the ones that are most likely to keep their jobs (ie Cordero in Texas, Baez in Tampa, Benitez in Florida). Since Yahoo does a horrible job at rating closers, you may get a good deal getting a solid closer for a borderline starter, rather than going for a dominating closer.
Despite what I said above, I think the trade you mentioned is still worth investigating because Soriano is a top 5 overall player at a postion with no depth.