I don't know much about the UKC registry, so take my opinion for what it's worth.
My boxer Charlie had an AKC ILP, which was like a limited registration (not exactly, but similar). I didn't have a regular registration on him because his parents only had the litter registration (apparently, the breeder demanded proof of spay/neuter before allowing registration, or something like that).
It allowed me to show him at obedience matches, rally, and stuff like that. He was ineligible for conformation shows.
All I had to do was provide photos (front/side/rear), provide proof of neutering, fill out the paperwork, and pay the fee.
I thought it was worth it, because he was not breeding material anyway (wry mouth, among other things), but I did want to show obedience with him so it served my purpose. It was not expensive, IIRC.
It depends on whether you need it on if its going to be worth it or not. If you have an altered dog that you would like to compete in Limited UKC events then yes its worth it. If you have a house pet that you don't have interest in doing anything with then no its pointless.
Think yall. Comfomation means little to nothing. Work is everything but still would the lack of this registry really hinder my dogs as far as performance titles go. That being said ive had a great deal of "mutts" out perform pure apbts ( catch dogs to be exact).