The electrical issues I had with my car (icons lit up, engine would momentarily stumble and actually died one time, radio would turn off) were caused by one of the battery cables being loose on the battery. An obvious problem but one that can be overlooked because it is so obvious. Another thing your dealer can try is to spray contact cleaner on all module and plug contacts. As alluded to by CrossfireLTD, over time corrosion may have developed on the contacts of electrical components and this may be cause of your problems. Also, methinks the 2005 upgrade to 2006 story is bunk and your dealer is just trying to stall you while he stumbles about for a solution.

As for a rental, you may ask if your dealer will cover the cost instead of going through Corporate. Mentioning "Lemon Law" may help with this. The last time my car was in for warranty work my dealer told me to keep the rental until they had my car fixed. My problems were entering the Lemon Law realm and I suspect my dealer knew this and wanted to keep me as happy as possible.

The dealers you talked to are right when they say that electrical problems like yours are rare. Far more common is that a component will permanently fail instead of working intermittently. And unfortunately, an intermittent operation is one of the most difficult problem to diagnose and correct.