My approach (and I think it's beyond criticism) is to try to promote with a team that
1) has at least a couple seasons left out of the big earners
2) has at least 2 or 3 homegrown and cheap backbone utility players with some trainability left
3) has enough cash to buy one player who is about the equal of the strongest player in a league.
That usually buys me at least one or two seasons of fighting for promotion to the next level. If I don't pull it off in that amount of time, I usually might as well sell off. The first season after promotion attendance bonus makes the first season at a new level your best shot at making a dominant team.