I haven't experienced any personality changes of this kind from long-term stimulant use.

A hypothesis about what happened to you: while the stimulants were effective, you got stuff done, which allowed you to shift your whole self-image towards "someone who gets stuff done", thus resulting in a personality change as an indirect effect.

I tried caffeine in early 2011, in the form of plain coffee no more frequently than every third day (so as to avoid building up tolerance/addiction). It seemed to help, but I don't recall any strong evidence that it was better than placebo (and I typically just followed it up by spending the entire time of effect at a piano, which succeeded in getting people to approach me, but not much else).

This came after I'd been on Prozac for a couple months (again, effects may or may not have outperformed placebo, but was weaker than caffeine), which came after a few weeks' trial of Focalin (which appeared to help a ton at 5mg, then stopped being helpful when I went up to 10mg, and wasn't nearly as effective when I went back down to 5mg, which sounds like evidence that the first bit was placebo).