Buy some wedges definitely. A lot of the best players have 3 wedges in their bag - evenly spaced distance wise as suggested above (they exclude a fairway wood).
Also learn the Flop shot. It takes a while to get the hang of, but its good for chips from rough and bunker shots close to the hole. You can only play them with wedges so the point above is still relevant.
Putters - I am not so convinced about. I've bought pretty much every one on the way up, and as to whether they have improved my game, I am not convinced.
What improves your putting is practice. When you have played a whole lot of rounds, you will no doubt have had the same putt (or the same line) a number of times. If you miss it left one time, you know to aim further right the next etc.
However if you are determined to buy one, the daytona is probably best (you will need a few more credits though). But remember you will have it for the rest of your WGT career.
The important thing to remember about putters is what are the decrements from 30 ft down and do they match up to the putts you are normally having.
If you are consistently putting from more than 30ft, then you need to work on your approach shots, but that's another post altogether.