I have to ask though, putting aside the value of 2UR, objectively speaking would you still choose a 23 RCF over say a zupra with a tune or an IS500 with a supercharger?
Hmmm...not an easy question to answer. I have done bolt-ons and race tune on my RCF (stage 2 intake, full exhaust, ECU software tune, throttle controller, lightweight battery etc.), but it is all within the parameters of keeping it perfectly safe/reliable and not straining the engine. So, it is a rather "easy" 520 - 530 HP (435 - 440 whp) my car puts down as nothing strains the engine. It basically feels basically like stock with more noise, more response, more power and a stronger midrange.
In the cases you described above, if I were a single, young tuner (in who wanted to look to beating Nissan GTRs from a roll race etc.), I would have taken the Zupra with upgraded turbos and tune. Thing is, I have two kids and an extremely busy life and I get very little time to even drive so RCF is just a means to have a hobby and "decompress" and have fun doing some tweaks. I think RCF does really well at being a well-rounded package from the factory, which you can improve a decent amount with very small tweaks.
To be honest, if I wanted a used 2 seater to modify into a monster, a C6 Z06 Corvette would be more compelling than a Zupra.
Regarding S/C'ed IS500, it is a bit like the case of Supra above, but more compelling due to the practicality aspect, it could apply to not just my single life, but married life. If my car was my central focus and I was a very active part of the car community, it would be compelling to buy an IS500 and put $20K on supercharger, suspension, tires, wheels, brakes etc. to make a 650 - 700 whp monster.
Not sure if that answers your question, but I had to think long to come up with an answer since it is a scenario I never had thought about.