Well, I'm one that regrets paying the money. Not to say that the textures themselves aren't an improvement over default, but they won't magically make your default airports into payware versions. The building boxes are still boxes - just a bit more pretty - especially after dark. Jetways are good if you're parking at the ramps. Amazingly, control towers aren't touched at all, and most airfields have one.
I had Zinertek airport textures and uninstalled them as I thought REX looked much better in the adds.. These cost about half and are nearly as good, imho - certainly much better value. I wouldn't now pay extra for the REX version.
If you don't have Zinertek already, then you may think the improvement to your default boxes is worth the cost - some clearly do. If you already have Zinertek, don't bother is my advice.