I think you did pretty good if it is clean as it sounds. You'll have less problems with 2001 up E320 as compared to earlier models. It is a good handling car but paint job is lousy like most of all MBZ.
Can't speak to the price. I used Kelly Blue Book Trade-In Values plus around $1000 to arrive at a fair price, or go to Edmunds site to the Smart Shopper Forum -- I guess it would be a little late for that.
You did well for a wonderful driving, safe, and beautiful car that can give you many years of pleasure but ( as we all have found out ) can be a horribly demanding and tempermental mistress at times.
It needs attention and care, but in spite of our complaints, you'll probably find it usually isn't too impossible ( just a bit expensive at times )
Fortunately, with the extended coverage you can hopefully cover most of the failures with someone elses dollars.
I guess you did alright. I paid $20,000 for my 01 E320 4Matic Wagon. Black on black. It got Xenons, CD Changer. It too had 45,000 when I bought it. Now it had 53.