I already know how some are going to blather on about Win Buttons and other non-arguments, so just pretend you did and skip it.
The experience points required for TR'd characters are ridiculous. Stupidly so. As it stands, the benefits of TRing (a couple extra build point, shoddy past life feat) do not justify the XP cost. So I suggest, with big changes coming, that you do one of the following:
1. Reduce the amount required to level: First TR adds +5% to the XP required to level over a first life character. Each additional life adds another +5% to a maximum of +25%.
2. Bonus Feats: Characters receive a bonus feat at levels 4, 8, 12, 16, and 20 on each additional life.