No CF or 3B free agent worth a crap is going to sign with the Twins when 2 of the top 3 prospects in all of baseball are knocking on the Twins' door at those positions.
Thrylos is right about peoples' expectations of Buxton being a bit ambitious, though I disagree with him on the use of AFL stats as a basis. Still, at best, he'd be a September call-up in 2014 and even that is contingent on him having a second straight season where he exceeds expectations... and given the level of expectations, I'm not sure that's possible. But by June/July 2015, I think he'll be in Minnesota.
Anyway, point is, if you were a free agent CF or 3B good enough to sign at least a 2 year deal, would you sign with the Twins? Not me.
I'd take my chances with Hicks (who I do think will bounce back and have a productive season) in CF and Plouffe at 3B (unless/until Sano forces his way on to the field).
If you eliminate those two positions, as well as catcher (where I just don't see OFFENSIVE options better than Pinto available at this point), the number of positions where you could reasonably expect to upgrade are almost exhausted.
As I've written elsewhere, I think the offense will be a bit better in 2014 even without personnel changes from the outside.
LF and DH are wide open after this year. And I'm not as high on Hicks as you. He did well in AA by waiting for strikes. Well, he got strikes in the majors, and couldn't come close to making contact.
I agree on 3B.