I will say that, over the years, ESS has proven to be the most conservative company as far as pushing the envelope. With that said, FI and regular track usage will likely shorten the engine's lifespan. Street driving or occasional use? I don't see an issue and haven't heard of any. If street and occasional track use is what it will see then there is no need to read any further.
If you are in a hot climate and plan to regularly track the car, I think you need to address cooling capacity. IMO, should be addressed anyway for high service demand applications. If you are novice or intermediate driver, likely won't have much of an issue. In fact, your car will run cooler and longer because you won't have the engine pinned at the redline because you can't use all of the power. As you get to an more advanced level you WILL be much harder on the engine because now you will drop it down to 2nd in tight corners because you can control the car and attain much higher exit speeds. At some point, you will keep the needle pinned at redline.
IMO...At that point, FI is going to become a total PIA. The stock engine can withstand about 20 minutes of torture. I don't see how increasing the power 25%-33% without more cooling will help that. I can get my STOCK E90 M3 to pull redline after 17 minutes on a fast track with a 3/4 mile straight. If you are constantly running the car 8x per weekend at that level then I don't think your car will last very long. I could be wrong.
Look carefully at what people are driving in the different groups. You'll see the FI'd cars in beginner and intermediate groups. Look at the advanced level...you won't see too many. With the advanced group I drive with, I'm the only idiot with an aftermarket FI kit. Why? Because its less reliable, more expensive, and more of a PIA.
If I was going to keep the car indefinitely I'd go NA. For the reasons that the OP stated...you like the character of the car...why not maintain it?
EDIT: I see some companies running FI'd M3s on the track but that's different. They have the financial and technical resources to fix things. Then my next question...how long are those vendors going to keep that car? As long as you?