It's important in some respects, not so much in others.
I bought now because I wanted to experience the M3 at it's peak. It's most perfect form as a racecar daily driver. Sure the new one will be faster, more powerful, have slightly better fuel economy, be more gadgety, but it won't feel like a thoroughbred driver's car. I'm sure it will be excellent, but I wanted the last hoorah gas guzzler V8 F1 inspired engine. I'll be driving this one for years to come.
For those that bought the E9x M3 because they thought it would hold value better and want a collector or investment car, that seems pretty dumb and I don't think there are many of those folks out there.