M3 vs. modded 335 is a can of worms. 335 better fuel efficiency, lower insurance, and with mods can perform better. But resale of mods is bad.
I would love to get the upcoming M3 with turbo 6, especially if weight is under 3200 lbs.
But the supersport 335 will also be awesome. Ditto the super lightweight Z2. Great choices up ahead, makes one think twice about squandering $ that could be saved for a new car in a few years...
Smart thing to do is buy BMW stock now instead of buying mods, sell stock when you want new model. Alternatively, mod your car as you need new parts anyway over time, and keep it for many years.