Do they even make a difference? Of course they look "nifty" but modding it, without an intake manifold and heads, would it make a difference?

 

I picked up 5mph trap with a ported plenum and SLP runners

The best gain to be had is with the base thou and that was never changed

 

Yup porting the plenum is a nice free gain, which will help enhance the runners and base. Base does help wake things up nicely. I had no interest in switching to a HSR or MR, I wanted more low-mid power, so the runners/base were great additions in those regards. Also, it kept me from needing to upgrade gears or torque converter.