I figure that for 99.9% of the situations where I would need to fire my gun in self defense, I will not notice a difference between my FMJs and my JHPs as far as POI is concerned. I don't shoot enough to really notice the difference between ammo. So when I do practice, it's fine if I'm using FMJ.
With rounds on the weak end of JHP-acceptable (so .38 SPC, .380 ACP, 9mm), I think it's worth it to get the premium ammo. You are right, at worst it's like FMJ. But I want something known for reliable expansion and penetration, as opposed to something that might just zip through or expand too far and fail to penetrate. In the case of the .380, I decided it was worth it to just carry ball ammo.
The bigger and/or faster your bullets go, the easier it is for the bullet engineers to make them work properly. That, and a .40 or .45 failed-to-expand is better than a 9mm failed-to-expand. That's why I just carry generic JHPs in my bigger handguns. I practice with the slightly cheaper FMJs, and those have more similarities (that of course I don't have a subtle enough feel to notice).
This is just my opinion, of course. I've sort of set up a 3-tier system for handgun rounds:
Tier 1, use FMJ
Tier 2, use premium JHP
Tier 3, use generic JHP
9mm falls in Tier 2 for me. .38 and .380 are the upper end of Tier 1.