Welcome to NICO!
The 06/07 model years are the same body style, engine, gear box, and trim. They are essentially the same car.
I owned a 2007 M35 until last year when it was totaled by a drunk driver. It had nearly 100,000 miles. It had every option aside from the rear seat theater option and everything worked like new. It had no oil consumption, great acceleration, and it drove and performed perfectly with a great ride quality - no squeaks or rattles. .
Common problems: none that I am aware of
Fuel: 93 octane - though others here have used lower grades, Infiniti 'recommends' the higher octane.
Repairs: The only actual repair it needed was a starter after about 90,000 miles - the starter relay did not disengage, killing the battery. Since I purchased a warranty with the car, that starter and the battery cost me just over $100 instead of $600.
Engine check: I have never heard of flooring it anf getting a check engine light in any car so I can't help you there.
AUX: Remember these cars are approaching 10 years old and technology was not where it is today in those years. There are after-market options that you can install yourself which will provide newer features to match today's tech.
MPG: All of these modes (even newer ones) average between 6-19 mpg on regular non-motorway speeds. My 07 averaged 17 on surface streets and 24 on the motorway.
Repair costs: Every car will have expensive repairs regardless of the brand. Infiniti repairs are probably even higher compared to a cheaper car with less features and lower performance.
The key is regular oil / filter changes and proper maintenance of fluid changes, etc. If you race this car, abuse it by driving like a maniac, and ignore regular maintenance, it will cost you a fortune in repairs. If you take good care and do not abuse it on a daily basis, you can expect great reliability and fewer repairs.
As for the Inifiti G models. They are smaller, lighter, with much less refined interiors, but are also great cars. MPG is higher, but not alot higher. They have a more harsh (sporty) ride quality and are also very reliable if cared for properly.
Where to buy: I know you did not ask this, but Carmax. Why? I have purchased two Infiitis and one non-Infiniti from different carmax shops and all 3 times I had a great experience. I am currently looking at an Audi for the lovely Mrs, ready to pounce when the right year / model appears at a Carmax shop near me. The main reason I highly recommend them is the lack of a processing fee, and the optional warranty. Their warranty is the most complete one available - it beats the Infiniti warranty hands down by covering many more items for up to 120,000 miles or 5 years from date of purchase. They cost about $2,000 give or take and they can add the cost to your loan if you like. I paid cash, but was told it would add about $30 increase in monthly loan payments. I can take my cars to any Carmax shop and pay NO deductible, or take it to any Infiniti dealer and pay $50 deductible per repair. I just did a search for the model you like and found this:
http://www.carmax.com/enus/view-car/def ... lts%20page
**** I am NOT associated with, paid by, or any sort of rep for CarMax - just a very satisfied customer. A few of my mates have also purchased from them and are just as happy. ****
