I don't think it has to be dumbed down at all. The 'Average Joe' has no idea how the Dollar, Euro, Franc, or any other type of money works, yet he knows it does and accepts its use. All Bitcoin needs to do is inspire confidence to be successful. The only way to do that is to get it into more widespread use. Dumbing it down is not a prerequisite for its adoption.
Rage
Actually the average Joe does understand how dollars work: you keep them in a little thing in your pocket and then you had them to people to pay for stuff.
Bitcoins require a "wallet" that is really some sort of mysterious "file" that can't be found. Normal people cannot find files unless they are on the desktop or, for more sophisticated users, in the "My Documents" folder. Your bitcoin wallet is stored in a HIDDEN folder. Normal people will never be able to find their wallet files, even if they were forced to use bitcoin.
To buy with bitcoins you have to use "addresses" that are really long and often changing. That is pretty hard for a regular person to grasp. Also they are case-sensitive. Most people type in all caps or no caps. Very few people use mixed case unless writing something very important.