I have 04 RC with stock pipes and want PC. Is it wasted without different pipes?

I wouldn't say its wasted as it does help with the glitchy fueling a lot, but as the stock pipes are fairly restrictive, (to keep the noise down) fitting less restrictive cans in conjunction with your PC (and a relevant map) should release a few more ponies.
And each of the stock cans weighs as much as a GSXR(!) which is another good reason lose the stock items

HTH

I have 04 RC with stock pipes and want PC. Is it wasted without different pipes?

Depends what you're expecting, most people don't think it's a waste, but it won't make a huge difference in power with the stock pipes.