Remind me not to put a wood panel overlay in my Cherokee.
They are definately asking too much. Nice bird, but regardless, they cannot expect to get out what they THINK they put in. Honestly, without upgraded radio's and unless there were some major issues, what in the world do they think they have put into it?
My theory is they got hosed on a couple of annuals (note: don't use their mechanic for a pre-buy) and are trying to recoup that, the full price of the plane, maybe some new tires/brakes/etc....but since they have done nothing major to the engine, and the prop was on it, what have they done?
So....they are being unrealistic. You have a couple of choices. Take the AOPA evaluator with you, take some ads of other 152's in nice condition, and try to respectfully educate them with the price you are willing to pay. Don't insult them as everyone has a right to his or her delusion. If they say no, tell them thank you for your time, I am going to continue looking, but here is my number if you ever change your mind.
It may be too that they like having the airplane around, so see no immediate need, and figure if someone is willing to pay the price, fine. If not, they will keep it. That is valid too.
I am finding this same phenomenon with motorcycles right now. Winter is coming, and these crazy people want the same price for a 2006 (two model years old) as I can buy it for new. Why...because "that's what I paid for it". No concept of "value" and no concept of negotiating with the dealer. Sellers bad decisions do not justify me getting ripped off.