i have 94 altima with 144,000miles. do you think it's worth upgrading with high performance stuff. currently i have a stillen filter, high flow converter and 2.5 straight custom exhaust. i see in many website with the link to the turbonator website, does that really work and claim it increase hp to 35?

Absolutely NOT. It is a complete piece of junk, does nothing for performance. It is also a very risky installation apparently.. I read about how a guy installed one of those, and the dinky little plastic fan blade broke off in the intake and got sucked into the engine... yea.. you can imagine the rest.
But yea, do not bother with it, waste of time and money, and could cost you some serious repairs.