How to increase internal memory of the HTC Wildfire S finally?
You've said that you partitioned before installing link2sd but not before installing data2sd. data2sd also requires extra partition just like link2sd.

The reason link2sd being not effective is because it moves all but data to sd-card. If any of your app uses huge data it will fill your internal space quickly.

Try going to Settings -> Apps -> Sort by data size and see which apps are on top and try clearing their data. This will free some space for some time but also clear that particular app's data.

As you've pointed out installing Dalvik cache to SD would be best. In my custom ROM I've to open terminal and type a2sd install and supply option y,n,y. Most probably this will work with your ROM as well.