Why not do what guild wars 2 does with magic find percentage?
For those that don't know, they allow you to have well over 100% mf but all it does is increase the percentage of rarer materials and drips by the %*drop rate.
So say you had a 100%bonus to shiny appearance, that percentage would only increase the appearance of shiny by double. So something that was like 0.001% is now 0.002% or w.e. it works for gw2 to an extent. You could have those higher percentage numbers for higher donations as well.
Just an idea. Also this was directed to the original topic of the thread. Lol
