To me, the stock dye-sub PBT caps on my RF 87u, HHKB Pro 2, and IBM Model F and Model M boards are sublime. These tend to be rather smooth in texture and they maintain a dry feel. All these stock caps are quite thin. PBT doesn't have to be thick to be good. In fact, the thin caps seem to be part of the design of the Topre and IBM keyboards. It is as if the caps were tuned to their keyboards.
Finding the right "tuning" can be difficult with Cherry mx, and third-party keycap sets for these keyboards can vary quite a lot in texture, from those as smooth as ABS doubleshots to as rough as the pumice-like set that I got from Keycool.
Recently, I received my Granite set, which has to be one of the handsomest sets in existence. It has an intermediate texture, a bit on the rough side, but I like it. However, I am having trouble typing on the Granite set because I am not accustomed to a flat profile or spherical tops on the keys.
One of the best values in PBT keycaps are the Leopold sets from a Korean vendor on eBay. The caps are very well made and fit snugly but not too tightly on the stems. There is no detectable warp, even on the spacebar. The texture is on the smooth side, but with the agreeable PBT dryness. The printed sets are lasered rather than dye-sub, as you would expect given the relatively low price. Unfortunately, I found that I cannot use these caps right out of the box on my WASD keyboard because the stabilizer wires rub on the inside front edge of the stabilized keycaps. The caps could be made to work by shaving/sanding, but I decided against doing this. Instead, I put a mix of two sets on my Novatouch -- dark navy blanks for the spacebar and mods; white front-printed for the alphanumeric keys and arrow keys. It looks great, and these PBT caps seem to be an excellent weight for the Novatouch, which I am typing on now.
All this is in answer to the OP's question, "[Are] PBT caps really worth it?" For me, definitely yes. Although I have some ABS doubleshots that look great, I very much prefer the feel of PBT. On the other hand, I like a high profile such as OEM, and while high-profile PBT sets exist, they are harder to find than lower profiles such as Cherry profile.