When one is about to be able to buy a new ship, there are various things to consider:
Finding a station that has the ship you want, preferably without "useless" equipment (hyperdrives, docking computers).
Finding a station that is near high-tech systems, so one can buy again high-tech equipment.
Consider the resell price of your current ship and its service level.
While the first two points can make the process of buying a new ship interesting, the last point is too me only problematic.
IIRC, the resell value of a ship is 70% of its base value. For a Cobra I it means that one loses 30K Cr when one buys a new ship. That's huge. And while one is looking for the new ship one wants the service level may decrease, which results in extra money loss (a few KCr).
As a result, it's more economical to wait longer and "upgrade" a Cobra I to a Cobra III rather than going from Cobra I to Moray, and then from Moray to Cobra III.
So my suggestions are:
Automatically include maintenance overhaul when selling a ship.
Be a lot more gentle with the resell value (like 90% of base value).
I don't think that core devs will make this change and it is not OXP-able due to the owned ship value in shipyard is displayed by the core game. But I can imagine an occasional ship customer (like in [wiki]SellAll[/wiki]) who just now gathered enough money to exchange his Adder to your actual ship and pay far better than the official dealers, sometimes even 100% of the maintained value plus equipment values. Then you could sell the Adder when you buy your wanted ship in shipyard, which mean a fix 19500cr cost for you (65000*0.3).
Î see that the service level property is R/W, and overhaul cost is 1% of ship value, so an OXP could fix part of the issue. Maybe I'll try my hand at inserting an entry in the F4 screen.
