From my very rough calculations I need to use my TT once a month to make it worth having. Over the last year that's been no problem at all. I don't actually keep track but I'd guess I've been out 20 nights in the last year.
I go between state parks and and RV parks depending on which kids and/or if I have my wife with me/us (wife likes the full hookups and cable TV - kids don't know any better :) )
Overall, there isn't a more economical way to get the kids out of the house to see world (or at least the world near us) than with an RV. I've bought and sold many cars/trucks/houses over the years and am usually left with a bitter feeling due what it ended up costing. I've never been anything but pleased with the value I get from my RVs.