If you installed just one of the components, you wouldn't feel a thing. But install all 3 at the same time, you should be able to feel the 10-15hp difference a little.
But you could definitely use that $300+ elsewhere. The best bang is going to be a 3.73 or 4.10 gear ($150-175), I would've said mid pipe, but i see where you said something about putting cats back on, so evidently you had an o/r pipe. Or get a nice shot of giggle juice. you can get a kit or system for about $375+. A 4.10 and maybe a 75hp shot of go-go juice, and you'll suprise a lot of more horsepowered cars from the jump
, until the bottle runs out...