Depends on how well it has been cared for. Generally speaking they are expensive to maintain. But on the other hand they tend to "go forever", so with care and attention they will serve you well. How is the bodywork - if it is free of rust, keep spending. If it has any rust, best to get rid of it.
It is a total waste.If you repair a part another may creep up causing endless expenditure for repairing.The spare parts for old madel may not available in market.
Certain classics might be worth repairing, but remember that newer cars are both safer and more energy-efficient. This is something worth considering when making your decision.
If this old Mercedes has low mileage and the body is in very good condition,by all means yes. Sooner or later this vehicle will be a classic car,then you can reap the benefits of selling it if you like,probably for a very pretty penny.
Continuing to repair an old Mercedes will cost more money than if you were to trade it in or buy a different car. Depending on your financial situation, I would recommend that if it is in acceptable running condition, sell the car and look for something newer and domestic.