Just a few thoughts based on my past experience buying and selling three planes so far . . .
I wouldn't sell it until you've found that perfect, absolutely fits the bill, got to have other plane that you are sure will fill that seller's remorse void. I'd also make absolutely sure this is the right move for you. Giving up that perfect plane (your 150) is not easy.
Selling and buying could also (very likely) cost you a bunch of money. I've found that transacting aircraft ownership, whether and buyer or a seller, tends to suck cash out of your pocket.
Finally, I know what you mean about a 172 not being as fun to fly as a 150/152. Ever think about a Grumman Traveler or Grumman Cheetah ? Fun, Fun, Fun. Just watch how you load up on a hot day - they are not as good climbers as a 172 is, plus make sure you get checked out in them as they can be different to land (notice I said different and not harder to land).
