As far as I'm concerned, if you are properly maintaining your 124 car with frequent oil and filter changes and other necessary PM items, your car is still a low mileage example.
Trying to predict when to sell ANY car before you have problems is like to trying to predict a womans response to something.
Even if something expensive does come up, these cars stay fixed after repairs. I personally believe that determining whether or not to do a repair to one of these cars based on its market value is the incorrect way to look at it. Even at high mileage, these cars remain reliable, solid and pleasant to drive. So, what would be wrong with putting some money into it and keep driving it.
The valve seals should solve your problem.
BTW, I'm personally very skeptical of these oils for high mileage cars. To begin with, yours is NOT a high mileage engine. When it starts, smoking, using a quart every few hundred miles and nothing can be done about it short of overhaul, then I will let you call it a high mileage engine. 'til that time comes use good quality oil of the correct weight for your climate.
Change oil hot and change oil often,