After visiting Mostar on my way back to Croatia I stopped to see Počitelj. I enjoyed the site but following Mostar it was a bit like having a digestive biscuit after a slice of chocolate cake.
It's quite small but enjoyable nonetheless, it's not a site I would head to if I wasn't already in the vicinity though, there's just not enough to make that worthwhile.
There's just a couple of shops catering for the tourist trade and you can wander around the narrow cobbled streets and take in the Turkish style architecture.
Just based on the site's size alone, I would be surprised if it made it to the full WHS list.