Well, because it won't eliminate the junk messages vying for my attention, it will just earn me fake email currency for reading them. This does not help the overall goal of email overload.
If I trust the person sending the message, he/she can just use the "Priority" feature. If I don't trust him/her, then I don't see why messages with more virtual currency units are necessarily more important than those with less.
If I trust the person sending the message, he/she can just use the "Priority" feature. If I don't trust him/her, then I don't see why messages with more virtual currency units are necessarily more important than those with less.