^ don't get it wrong, the M is a great car and being that you have the M35, you can still find a lot of parts to modify your car to add some fun to it... a lot of the M35 parts are interchangeable with the G35 (VQ35DE motor)...start checking out the classifieds section for G35's in this forum as well as countless others...I'd also check out 350Z forums as well.
From personal experience, I did a lot of research on the G35 because I was also thinking of getting one in addition to my M35, so I was pleasantly surprised to see a lot of parts available. For our cars, the common add-ons would be Uprev tune, Ztube, K&N drop in filter, plenum spacer, modified lower plenum (Motordyne MREV2), HFC's, exhaust set ups, TransGo shift kit. All of which are inexpensive when getting the majority of them off of G35's classifieds
Keep your car and enjoy it...do some mods and call it a day....I've got some mods and my car has approx 136K miles on it and it is still enjoyable....
...If you're going to go 'extreme' by going Force Induction, ITB, etc...then consider beefing up the engine....