That seems pretty expensive to me, too. A quick look on autotrader finds a bunch of better deals on F12s. This one has about half the miles--only 13K-- and is $9K less:
https://www.miniofpittsburgh.com/use...83a4abd58b.htm
There are several threads on here about warranties. If you want to transfer some of your risk it can be worth the money. As
mikerx5 says, if you have year from CPO that maybe enough. Certainly it gives you some time to assess.
Maybe a more important question is whether you should move toward the M6 or stick with the M4. They are really different cars. I think the M6 is a lot more special, but it is not the best choice for everyone. Look for the recent discussion started by a guy wondering if he should trade up from his M3.