Normally, given what what you are looking for, I would recommend you go for tighter string. At the upper ranges of the racquet's limits. I would also try some less elastic string if that doesn't get you where you want to be.
But what you've got there is a Weezer Special. A senior citizen doubles racquet. Quite possibly the worst racquet you could have chosen if you want to stay on the baseline.
So, the store is open, go get yourself a racquet. Anything will be better for what you want than that one. Stay in the 95-100 range if you can. Also, for baseliners I think heavier frames are better than lighter ones. It does depend on what kind of baseliner you are.
Look at some of the Prince Speedport frames. The O3 Hybrid tour is pretty close to the overall feel of the Wilson Hyper Hammer. Also the Speedport Black which is a larger headsize. The Head MicroGel Prestige Mid will have a similar feel as well. These are all frames that have about the same flex and swingweight as your current racquet, but are heavier players racquets with smaller head sizes.
Now, if you aren't fond of the swingweight or flex of your Hyper Hammer, You can pretty much pick up any midsized frame and it would be better for groundstroking than the one you have.
I'm not sure if someone in this thread mentioned it, but demoing racquets is your best bet. If there is a tennis shop nearby, see if they have a demo program. Typically they let you take 2 or 3 racquets for 3 days and charge you $15 to try them out. Pick at least one that's heavier, one that's lighter and see how they feel. When it comes to buying most will take the demo cost off the price of the racquet if you choose one you've demoed. If you can't find a store nearby take a look at Tennis Warehouse's demo program. They will send you 3 racquets to try at a time. Mail back them back and try a few more.
