Chronic MDMA use causes a decrease in concentration of serotonin transporters.

Lottery winners end up no where near as happy, long-term, as they imagined they would be when they bought the ticket (Brickman, Coates, Janoff-Bulman 1978).

This is weak evidence, but it suggests that wire-heading in practice isn't going to look like it does in the thought experiment - I imagine neural down-regulation would play a part.