I've spent a lot of time on this section of the forums. Not surprised this conversation is still going on.
I've owned the M235i and now an M2 so here is my experience.
I spent a lot of money on my M235i. Enough money for a Dinan badge, was considering getting an LSD, a stage 2 tune, and the exhaust from the M2 someone was selling on here. I remember researching ways to alter my rear valance to fit the quad tailpipes.
I realize now I was trying to make my M235i into an M2 or as close to it as I could. I also made the mistake of test driving the M2 and comparing it to my modded M235i. I didn't even push the M2 that hard.
To make a long story short. Life is short, and I think you should just get what you want. If you're happy with the M235i/M240 and don't want to spend the money on the M2, that's awesome, enjoy your car. They're great cars.
For me, I really like the look and styling of the M2, and it's what I wanted deep down from the beginning. The only mods I'm doing is an MPE and drop-in air filter. I'm fine with the car the way it is. I don't care about the extra money because it's what I wanted.
On how the driving characteristics compare. I did one HPDE in my M235i, and picked my M2 up at the performance center. From the short course at the BMW performance center I could tell the M2 was different, almost scary different. You can really push the car and it complies.