Depends on how you value money, and see 'value'. The M3 is an incredible car, but even purists will say that they aren't what they used to be. Unfortunately, MY17 BMW's are going away from their extensive car maintenance. So, that should be factored in as well.
The one BMW I wish I could own is an M3, and if I had to choose between the two, with money not being an option, I'd definitely be torn. That being said, an absolutely loaded, bonkers GT, would be hard to say no to.
Also, I wanted a C7 for a while, until I stalked a few forums and saw A LOT of people complain about reliability issues. Sure, it's a performance car, it's going to happen, but being so new, some of these issues shouldn't.
The 4.0 V8 is known to have rod bearing problems.
If you do a search you'll find a lot of information about it.
BMW Motorsport engines require some pretty intensive maintenance. The rod bearings on the S65 engines don’t last anywhere near as long as they should. It would suck to own such as expensive engine, but have to worry about rod bearing failures everytime you drive it hard.
I agree with everyone else, you might need to just think on it for a while and narrow down your list a lot although it sounds an awful lot like you're dying to have that M3.
I don't agree with the buying a house idea, and nearly anyone who has suffered from the last housing market flip will tell you the same thing. The house I rent now was "cheap" back in the mid 2000's and is now upside down by over 50 grand in a neighborhood that is going downhill fast with an influx of state-sponsored residents. There is no way it will ever in the next 20 years be worth enough for it to be sold which is why its being rented. The days of buying a house as an investment to drop when you're ready to retire are pretty much long gone unless you have enough liquid assets to do a quick fix and flip, and you have to worry about increasingly high property taxes in most areas. Homeowners insurance, maintenance, heating, fixing all of the little problems that pop up. Renting sounds like throwing money away but it gives you a much less expensive and stressful day to day life, especially if you're liable to move at any time in the next 10-20 years, and most of the people I know are desperately trying to get out of their houses and into a decent condo or apartment. Just my .02 on the issue.