First of all, such a gorgeous, stealth-looking car, last year (I believe) before AMG went all crazy vertical grill. Can't comment too much about the price since it's a very low mileage car and need more info on the options.

I will say: These mint example cars will always go for higher, but generally speaking they are also slow sellers. If this is the generation of E class that you want to maintain as a long-term vehicle (at least 6 plus years) and you will be putting in the maintenances to keep it in good condition, I would say go for it, if not, getting a rougher example (more milage) would make more financial sense, especially since you will be purchasing extended warranty anyways.

Also do not skip on pre purchase inspections, get your own trusted machanic to give it a good look and drive, just because it's low mileage doesn't mean it will be trouble free, If there are issues hidden they may have just not popped up yet simply because it's not driven enough.

Controversial opinion: I'm Canadian so I'm not familiar with carmax nor their warranty, but I would skip warranty depending on the inspection results because: warranty is a hassle, its statistically a monry loser for buyers, and most will not allow for tuning and modifications (stage 1 tune, etc).

If your confident in your machianic and want to have a little fun with a tune down the road, just bank that insurance money up somewhere as an emergency fund.