The unit you are buying needs new tires if they are over 5-6 years old. No matter how much tread and how much the salesman tries to BS THE RIG NEEDS NEW TIRES.
As for going from a 2007 to an earlier rig. You know the mechanical condition of your class C but do not have any History on the proposed unit.
I own an older rig that I bought used and it doesn't bother me to buy used BUT going backwards is not a good thing.
Also make sure a predelivery inspection is done and those items needing repair are fixed BEFORE I REPEAT BEFORE you give them the balance.
Once you pay you are like yesterdays newspaper to the dealership.
What worries me the most is the kind of repair you will get for the chewed wires. Will it be splice and tape or new wire from beginning to end with no splice this needs to be spelled out in the contract to purchase.
Since you state "We now do more near home camping rather than long stretches and stay for a wk. or two"
Wouldn't an add a room be more beneficial allowing you under the awning without the bugs.
If I was in the situation you are and my class C was okay mechanically I would keep it
