I prefer complete rebuilds. For me, i have to start from scratch. In most cases, i have changed the sets too. I have 3 teams now, and i wanted to tamper with every set (the only one i don't have is a Fastbreak team. But I'm on my way to picking up a 4th and I'll change to Fastbreak with them).
I've just begun all this like a month ago real time. Except for one team, which is now competing. And yes it's "expensive" to rebuild, but i don't call it a waste of time. I enjoy it step by step.
The MAIN reason i rebuild, I've signed up for 2 good teams since I returned. And i quit them both after that 1st season. One, i was the #2 team most of the season, got a 1 seed in the NT and made the E8 (losing in OT in that game, errrrrr). BUT....
I had absolutely NO connection to that team. I made adjustments every night, but had i not, i wouldn't have cared. Winning in that manner was extremely boring to me, because i didn't build it.
I can tell you every thing about every player on every team i have, by memory. Even most of the guys that have graduated from my rebuilds. But the team's i took over that were already good, i can't remember even 1 players name. And maybe I'm different, but that kind of thing matters to me. It's just more fun for me.