Tips on Buying Cars: Demo, 2007 nissan murano, nissan murano

Question
I am thinking of trading my my 2007 Nissan Murano, which I owe $26,000 on, for a 2009 Nissan Altima demo with 5,000 miles on it.  All of the places I have gone to value my trade are giving me $18,000.  Nissan asked if I would leave my car there because a wholesale dealer was coming and they would detail it to see if they could get $22,000.  That still leaves me $4,000 upside down.  But, I did purchase an extended warranty and extended service agreement which I can get back and apply towards principal.  The car I am looking at is a demo, and it has 5,000 miles on it.  Nissan has offered me $1000 rebate, deducted from invoice.  I feel like there should be a compensation for the 5,000 miles, otherwise I would just purchase a new one for $300 over invoice, right?

Answer
First the dealer wants you to leave the vehicle there is just a ploy. They know how much you will get for it. Cleaning it has nothing to do with it. Remember every $1000 you roll into a new loan will increase your payment about $25. I'd consider a lease.