Currently at about 52k miles in an 08 G35x. Wondering what maintenance should be done (or should have already been done) at this point other than oil changes, or what should be done in the near future. Thanks in advance for advice. Thanks!

Trans drain and fill at 30k air filters in cabin filters. 60k is the next big one. Trans drain and fill, cabin filter rear diff fluid change coolant flush. Check your owners manual for all the recommended maintenance

Drain and fill or flush? Wouldn't flush be better?

Along with what was mentioned above, you're approaching time to replace drive belts also. It's a 30K mile replacement though some folks haven't as far a 45-50K. Your choice here.......

At 50k I had the cabin filter, tranny drain, rear diff fluid and coolant flush. I eyed my drive belt at 30k and 45k and it was fine. I didn't have it changed till 60k and even then it looked fine.

I was planning on doing a that 30k maintenance at 50k. I inspect my own belt.