the rust is only on the bracket as rest of it is plastic, i think you should keep everything as is for now, as you have sorted your problems, now enjoy.
n75j valve can/does give a greater pickup on the boost and also sometimes a slightly higher boost.
the advice from expert tuners is to keep the standard valve in there, that is what your map has been designed around. n75j valves can sometimes cause the car to hit it's boost cut. also you want to make sure you don't over boost without enough fuelling/incorrect timing. so if you have any other boost related issues you have introduced a potential problem, thus making fault finding a greater issue.
whether you get one is upto you though.
now on mine, i have introduced a mechanical bleed valve just after the n75c (standard) valve to raise boost pressure. I MUST WARN YOU, that this is done at your own risk, you have to be sensible here!, i have spent money on getting my engine mechanicals up to handle extra BHP and have lower compression pistons which will help reduce chance of pinking. but my fueling maybe out and i may blow a hole in a piston. hence you do it at your own risk.
to some up though i think i would save the money, and maybe save for a k04 in the future, then remap for that. you could see 240bhp probably and that should be enough to keep you happy for a while.
