I think it depends a lot on your flying patterns.

For me, my travel used to be primarily domestic, and I had a paid membership. Now, my travel is primarily international, and with the added benefit of time that has brought me lifetime *G status, there's no reason to have a paid membership. For the odd time that I am flying on a purely domestic itinerary, I have a couple of passes from a co-branded credit card, and I almost never use both.

If your spending patterns mean an extra 500 PQP for every $12K on a credit card would make a difference to elite qualification, then it would seem to make sense to move your credit card to a UC co-branded offering.

Like many others, I'm of the opinion that the biggest benefit to UC access is using the agents inside the club durring IRROPS. It's like insurance: you groan about the costs when you don't need it, but are immensely grateful you made the payments when you do.