I started my campaign when 3.0 was first coming out, converting from 3.0 to 3.5 when that came out. We started at 1st, and now the characters are 13th and among the most powerful (in terms of level) in the civilized lands. And I could easily run them for another five years.
If I've run for the characters since low level, I have no problems running at high levels. It's not "crazy amounts of abilities", it's incrementally adding on additional abilities to something I already know. By the time next level comes by, it's the same.
Now, I seem to have slow level advancement compared to some, giving me more time with the characters at each level. Plus as a player in various games (including one epic) I'm used to what's out there and what works for when I'm creating/running high level NPCs.
Cheers,
Blue