This has been brought up
so often, I'm surprised we don't have a sticky for it...(no sarcasm.

)
I'll assume you didn't do a search beforehand, but if you're up to some additional reading and research, here are some other threads to poke your head into:
http://www.infinitiq50.org/forum/new-2014-q50-general-discussion-forum/777-sport-vs-premium.html
http://www.infinitiq50.org/forum/ne...ion-forum/321-difference-sport-non-sport.html
http://www.infinitiq50.org/forum/wh...770-comparing-sport-suspension-non-sport.html
http://www.infinitiq50.org/forum/ne...3953-help-premium-vs-sport-seats-fascias.html
http://www.infinitiq50.org/forum/ne...brid-sport-vs-non-sport-braking-handling.html
I'll also add in my two cents. The Sport model, is where the Q50 shines in terms of performance. If you're a spirited driver of any kind, who likes curvy roads, fast turns, quick lane changing, and whatnot, getting the S is what you should go with hands-down.
If you've ever driven the G37 or a G37s, the Q50 and Q50S are not quite the same. The non-Sport Q50 rides a like softer than the outgoing non-Sport G37. This also means more body lean and a little less control during spirited driving in the non-Sport non-Hybrid Q50.
The cosmetic/mechanical upgrades of the Sport model, for me, definitely justify its price.
This includes the aforementioned Sport suspension first and foremost, which definitely goes a long way;
Then of course, there's the sport front bumper, which I think compliments the Q50 very well--it also provides a more unique, aggressive, and sporty look;
Then there's the large sport brakes, which are powerful and have saved my skin in more than one occasion;
The magnesium paddle shifters, which function very well and look great;
The aluminum pedals, which are sexy and sporty;
The large 19" sport wheels, which are a bargain on the sport model and would be pretty costly by themselves as an add-on;
Last, but not least, are the lovely sport SEATS which hug you right in without feeling too snug and tight and includes the nice thigh extenders for increased comfort.