I dont know about the A320 but until we get the 737 Max next spring , there is no difference with regards to the fuel efficiency of the new -800 we have and the 15 year old I flew this week.
So for the BossMan it is worth more as he has already payed it of several times, engines are new and if he keeps it until just before it pulls an AlohaAirlines it is a pure cash cow.
I do not know how C and D checks effects the money game, but the cow hide seats and yellow plastic is indestructible, so is the loo.
Now I got curios, need to check into this.
The trick I have heard is to keep them in the air with pax to destination.
Even an old Norseman has value , when well maintained , Ask any Canadian.
Here comes my wife, I shall ask her.
Regards
Cpt B