Hate to respond to a several month old thread, but I ran across and was wondering if you ever had this work done?
I ask because I have a 35 year old pool and when I had it refinished 8 years ago (maybe 9 or 10-time flies!!!) I wanted to do exactly what you are wanting to do. Here came the catch--the original Kool Crete got its cooling properties from ASBESTOS!!! So, the bad news is that anything it was replaced with would not stay as cool in the Texas heat. The worse news, most places would not even touch the job of removing the old. Those that did, said it would be an expensive process because unless you find someone working under the radar and willing to skirt the regulations, there is federal red tape involved in any project that requires asbestos removal.
Now you said 20-30 years old. If it is 20, it may not be the original stuff and no worries. If it is 30, it very well could be the original stuff and there could be complications and more cost than you expect. Certainly, if you go back to your original plan and try to tackle yourself, make sure you know what the stuff is and you protect yourself with proper respirators. As you may well know, the last thing you want is to inhale asbestos fibers into your lungs.
Me, I ended up patching the bad areas as best I could with some concrete patch and grabbed some garage floor stain from HDepot and painted that sucker. It needs a recoat every 3 years but it really looks pretty good. I am pretty picky and notice the less than perfect areas. But few others do--in fact, when I slap a fresh coat on, everyone just compliments it and wonders if I had it refinished. Plus it is cheap. Less than $100 and a couple of hours every three years and you are good to go. Just be sure to buy the non-slip additive and add it so that the new coating is not slippery when wet. I think Lowe's, Sherwin-Williams, and most other major brands and stores sell similar product if you have a brand or store preference.
Just my two cents from my experience...
Paul