Just like buying any non-M Zed you really need to expect to have to replace things irrespective of mileage and/or condition. A high mileage car isn't a terrible proposition if you invest plenty of time on research, and then budget for things which either haven't been done or aren't in the service history. Picking with what Pingu says about cheap inspection services I totally agree, and these are the things you need to research - the general cost of ownership. You can of course take your new M in to any old garage for servicing, but the engines require specialised procedures so likely they'll just change your oil and filter and pat you on the back. I know my next service will be expensive as it will need the valve shims checked.
With what you are searching for you not only have to budget for the initial car, but also the increased cost of "M" related parts. "M tax" has become a meme recently but there is a serious side to it, most of the parts are just more expensive than non-M versions. In some instances you can find cheaper non-OE parts of course. Spend some time on realoem and paste random part numbers in to eBay and compare them with what you know you've changed on your previous 3.0.
Sorry if that all sounds patronising, and I'm not trying to put you off just giving some of my recent thoughts. I'm experiencing this first hand, didn't ever see myself becoming an M owner, but I now am. So, big outlay for car, expensive OE parts and expensive specialist servicing. It's been a real eye opener these last 6 weeks. Do I regret it? Hell no! Well, not yet anyway