is it irrational?
 

I have a 2010 base black 6 speed with 38k miles. The Nissan dealer has a black 2014 new base automatic. I love the z and its probably going to be my last sports car, since I am 66. I do not find any other sports car attractive.

My car has the normal wear and tear of a 4 year old car. Still looks pretty good, dries great.

I am increasingly tempted by the new 2014Z.

Dealer willing to trade, says my book value is about $18.5k, he would trade for a $10 k difference.

Since its going to be my last, should I?

Yea probably is. You are just getting the same kind of car with a different transmission is all and losing 10 grand for it. Not worth it in my opinion. Since this will be your last car, look at the corvettes a bit. That is what I would do if I decided to trade my Z. Almost did actually! lol

My first reaction is that if this going to be your last why not do it right and get something with comfort and spring for Touring at least?

I agree with falcon. There is not enough of a difference between the models you are discussing to make that a rational trade. If you were talking about going from a base to a loaded touring, that would be different.