We purchased the Zone Camping Pass (Southwest) for about $500 in 2011 and tent-camped at various campgrounds to save on hotels while visiting surrounding areas. After camping just a few times, the pass paid for itself. Very nice to have showers and other conveniences in a reasonably secure setting. In the colder months, we put the tent away and used rentals units (cabins, trailers), which still were much cheaper than hotels and even more convenient, though our first trailer was very run down and had a hole in the roof.
As for the Tent Camping Pass (TCP), it is about $250 at the time of this writing, and may be worth considering. In fact, we purchased one (and cancelled it; more below) earlier this year (2013). However, understand that YOU CAN'T RESERVE TRAILERS AND CABINS with this pass. I understand their reasoning behind this given the limited number of units, but it is a huge restriction, and Thousand Trails needs to put this up front and make it clear. The contract seems to imply that you can reserve the rental units, but you can't, as we only found out after the online system rejected our reservation. On the plus side, Thousand Trails were good about refunding the TCP fee and cancelling our Zone Camping Pass as requested, so doing business with them was not an issue. Be sure to read the contract for where and when to send your written cancellation request (i.e. letter).