I think the main difference is that since Windsor Palms is older, there is more variation in the quality of the accomodations. Meaning that some at Windsor Palms have been kept up very well and may have even had a recent refurbishment so that they're extremely nice, but others may have not been well-maintained and are appearing somewhat run-down.
But, I'll also say that even at the newer Windsor Hills, there are some places that were only outfitted with the cheapest, most basic furnishings and those may already be appearing run-down.
I'd say in general, that Windsor Hills is likely to have things like flat screen tv's while those would be a fairly recent addition at Windsor Palms.
We've stayed at both many times and would (& will be!) go back to either. The surrounding area is basically identical, as only about a mile separates them on 192 (I think), so you use the same grocery, restaurants, etc for either.
We don't use the clubhouse or pool at either one, so I can't comment other than the obvious that there's a slide at Windsor Hills and not at Windsor Palms.
We're going back to Windsor Palms for Thanksgiving and staying in a townhome that was recently sold and renovated!