For me, the mechanic has worked out well. Early in game, they're precious and rare, and so you're prevented from being too overpowered too quickly and too often (scaling power armor models also helps with this). Mid-game now, I'm with the BoS, have T-60d PA and about 30 cores, and all three Science perks extending their life. I am no longer worried about running out out of cores any time soon, which is good because I'm a BoS Knight and do most of my missions in my PA. At the same time, I have few enough that I'm not taking my PA for granted and am not going to go around wearing it unnecessarily. Eventually by the end of the main quest I'm sure cores won't even be an afterthought, but that's okay, too, because at that point I feel I've "earned" being overpowered.
So I'm totally cool with the system.
Edit: The need to repair parts also helps balance things out.