A major service on the SL will probably be in the neighborhood of 500.00, I would imagine the corvette is about the same. The 4k figure is on the two exotic cars you mentioned(probably more). I was hot and heavy and almost ready to purchase a 1988 Ferrari 328gts until I found out what a major service costs.
If 1/4 mile times, stright line acceleration and horsepower is all you want then the corvette is your ride. Like I said you need to drive both of them and judge them by your own criteria.