From a broad strategic perspective, I'd rather use the funds available to add to payroll to pick up talent via the FA market than to trade away assets for other players. As a corollary, I would control risk by diversifying and avoiding contracts longer than four years, and would sign three or four second-tier free agents (ie those without a qualifying offer) than go after the big names with qualifying offers.
The main areas to upgrade are third (options are Prado, Freese, Turner) and catcher (Jason Castro is my first choice). I would also spend some funds to build a strong bench and possibly sign a reliever with a track record of success to help out in high leverage situations.