I have a 2012 Sport with Navi, paid roughly $30k back in July/August of 2012. It has 18k miles on it and KBB shows a value of roughly $24-25k for excellent trade in, about the same as a G37x of the same year and mileage. My area has a lot of G37x's around. I found a few G37xS with the roughly the same mileage and same year listed around $26-28k, which I believe I could pick up for around $25k. Would it be wise to go with an even trade? Not 100% sure what to do, have my eye on the 2015 Maxima but not 100% sure of that either.

Sounds like a good trade to me. I would go for it if it were in the shape my maxima is in. I too have a 12 sport/tech with 15k on it. Always garaged.

I don't think it is possible for you to do a straight trade.
A dealership has no incentive to just swap cars, so will spend a minimum of $500, and up to $3k there.
You could try to sell your car, then purchase a G37, but again, you are going to end up spending money.

There is a slim chance you could make it work, but it is probably near impossible.

This exactly. Also either way you cut it; the Infiniti would hold more value than the Maxima. I couldn't see them doing a straight trade on a vehicle they would potentially lose money on.