The first thing I'd do is make sure you have good cooling on the trans fluid. I'm now running a Setrab 19-row Series-6 width cooler for my trans fluid, and I believe it's enough to keep from cooking the fluid under pretty extreme conditions. Most of the kits from the vendors have smaller cores than that. Somewhere deeper in my journal there's some posts about that (e.g. don't buy Stillen's kit, just buy a completely different set of adapters and hoses anyways, because their lines are too large to clamp onto our trans fluid fittings securely - not sure about GTM's).
Keeping the rest of the car cool (e.g. radiator upgrades, uprev fan settings, large engine oil cooler, maybe vent the hood near the front of the engine block, etc) is critical as well, since all temps on the car are somewhat interrelated.
I haven't ever done any trans-parts upgrades aside from cooling. I passed on the GTM valve body job for now because I couldn't get any reliable information on how it behaved from a road-racing perspective (i.e. whether it makes the upshifts too "shocky" for breaking traction on upshifts during trackout (or downshifts while trailing in) - I imagine some street guys and drag racers might actually like that behavior, but I sure wouldn't). I've never even considered touching the torque convertor or anything like that, although after this incident the HD Flex Plate is a little tempting.
Upping 7AT line pressures just a little bit via UpRev is worth it, but don't go too far. ~10% bumps across the board worked well for me with boltons. I also ended up switching my fluid to Motul Multi-ATF, which is one of the very few aftermarket fluids that's rated for our trans from a reputable company. I think it's at least as good as the stock fluid at handling the stress, anecdotally, and I've had it in for a couple of change intervals now. But if you care about dealership warranty issues, who knows if they might balk about using anything but official Nissan Matic-S. GTM has a couple of different PDFs on 7AT fluid swaps and recommended change intervals based on trans fluid temp. Putting in a trans fluid temp gauge (in the side of the pan) is worth it, especially one with a peak hold to find out your high-temp marks for the day. Check out this one:
http://www.gtmotorsports.com/Manuals..._Procedure.pdf
At 4 track days a year, you'll be long done with that car before you've put as much wear on it as I have on mine, so you're probably going to be ok if you're reasonably cautious. I was reviewing my records on this stuff a couple months ago, and me and this car have been through about 38 track days in just a little under 3 years (or ~19x full track weekends if you prefer to count it that way). So that's a rough average of a little better than one weekend every two months for the whole 3-year period, plus another ~40K of street miles from back when this car was dual-purpose. Track miles are hard on any car. Having a major failure by this point is not completely unwarranted
