I think the "fit" is going to be Nate Clements. He's a physical corner, good in run support, thrives on playing close to the WR. He fits in perfectly with Gibbs Cover-1 schemes and makes a good pair with McKenzie.
But he is the only player i'd "splurge" on. Beyond that, veteran depth is all I would go for in FA.
The problem with acquiring players in FA is you have to overpay to do so. If you have a critical need or it's a difficult to fill a spot (CB and QB go in the latter catagory) then you do what you need to do. But if possible it's always better to build by drafting, because rookies (other then top 10 picks) are invariably cheaper and you can get a discount on resigning the in the future.