The biggest problem I see with it is that as the party continues to gain levels, the characters at lower levels would be gaining MORE experience than the rest of the party. So, I don't know that it actually solves anything.
So the party Wizard needs to save up his experience in order to gain purely Tier 1 levels. Once the rest of the party (Warblade, Factotum, Binder) has reached 4th level (10000 xp total), the Wizard is still 3rd level - 2000 away from 4th. The Wizard is going to start gaining more XP from combats than the rest of the party. He's two encounters from 4th level while the rest of the party is roughly five encounters from 5th level.
If the math sticks, the party won't ever be a full level ahead of the Wizard until 17th level. It doesn't seem to be a significant enough impact to "balance" the game, if that's what you're after.
Old Char Lv Tier 1 Tier 2 Tier 3 Tier 4 Tier 5 Tier 6
1st 1600 1300 1000 800 700 500
Starting with a table like that might make it a significant enough difference to really change the scope of the game. I still don't know how well "balanced" the result will be, but at least there should be a significant change.
(The math)
[spoiler]At 15k XP, the Warblade, Factotum, and Binder are at 5th level. However, the Wizard is sitting on 15.3k XP and at 4th level (needing 2.7 to make it to 6th). Again, the Wizard needs roughly two encounters to reach 5th, while the rest of the party will reach 6th level in roughly four encounters.
At 21k XP, the Warblade, Factotum, and Binder are at 6th level. However, the Wizard is sitting on 21.5k XP and at 5th level (needing 3.7 to make it to 6th). Again, the Wizard needs roughly two encounters to reach 6th, while the rest of the party will reach 7th in roughly four encounters.
At 28k XP, the Warblade, Factotum, and Binder are at 7th level. However, the Wizard is sitting on 29.4k XP and at 6th level (needing 4k to make it to 7th). Again, in two encounters the Wizard will catch up, but the rest of the party will break away in four encounters.
At 36k XP, the party will be at 8th level, except the Wizard who sits on 37.6k XP and 7th level (needing 5.6 to make it to 8th). In two encounters the Wizard will catch up.
At 45k XP, the party will be at 9th level, except the Wizard who sits on 47.1k XP and 8th level (needing 6.9 to make 9th). In two encounters the Wizard will catch up.
At 55k XP, the party will be at 10th level, except the Wizard who sits on 56.9k XP and 9th level (needing 9.1 to make 10th). This is where it finally breaks. The Wizard needs three encounters to reach 10th level, while the rest of the party still makes 11th in four encounters.[/spoiler]