Welcome to NICO.
I found a few posts similar to your situation.
zerothread?id=141231
zerothread?id=51477
You definitely need to get the reprogram done; and even after that, you may find that the bank 1 Cat is bad.
As for warranty coverage: I've worked as a warranty administrator for about 3 years (covering 4 different car lines). The Nissan dealership you took your vehicle to in #3 took your money, plain and simple. The Maximas have the exact same recall as the I30, and have the exact same parts (ECM and Cat). There is no valid reason that they didn't perform the work.
Both the ECM and the Cat are covered under your emissions warranty (7/70k Cali - 8/80k Fed) and the TSB should be performed at no cost to you.
Take your car to the Inifiniti dealer. Don't go in complaining about the bad experiences you've had so far, that was none of their doing. Just tell them about the code and that you know that there is a TSB related to this problem. Remeber you can catch more flies with honey than with vinegar.
As for the Nissan dealer mentioned above, I would contact Nissan Cunsumer Affairs and see if they can negotiate with the dealer on your behalf to get a refund. They may tell you too bad; but if it was me, I'd give it a shot.
Nissan Consumer Affairs P.O. Box 191Gardena, CA 90248(800) NISSAN-1 (or 800-647-7261)9:00 a.m. - 6:00 p.m. Eastern / Central Time8:00 a.m. - 5:00 p.m. Pacific TimeMonday through Friday