I'd rather propose bonus DP for higher donations.
Wouldn't hurt anybody.
One issue I have with the tiers: I had several people donating $2 * 3, which won't get Kyuubi. Hence I don't really like the step-idea.
I wouldn't give away stuff you'd also get for DP - would defeat the purpose.
Either we'd give out stuff that is special / not bought with DP, or we just give out "extras".
"Extras" are very easy to program into the current system.
So we'll call them 'extras' however I've brought this up before. DP is USELESS due to the kg enabling dk'ing multiple times in a gameday. It wouldn't suffice.
DP is not useless for those who do not have all of those KG's. Like all the new players that would keep the game fresh.
Though, if you find DP so pointless, if you got any, I sure as heck could use some. My stock is starting to get kind of low.
On topic, giving extra DP would be easier to implement if it also included the kyuubi (presuming that kyuubi is lowest tier and the new tiers would be above that). Something a little more challenging would be the mercenaries, or even a different special mount, with kyuubi switching to the higher end of the tiers.