I have spent a tremendous amount of cash on various pony items that I've lost track. Strangly, I never seem to really use or play with them. I have collected about 5 different MLP shirts to this date, a Princess Celestia plush, and some minor toys.
I regret the clothes because the artwork on them gradually disintegrate no matter how carefully I wash them. Not to mention they're horrifically overpriced. The Celestia plush was worth over half a grand and she's just sitting on my desk. I still love her dearly regardless of price (who comes up with these insane price tags?) At least she's holding up nicely to this date