I just did this in my 67 C-10 and can't really tell the difference, but I've converted to an internally regulated alternator. Also, I live in the big city with lot's of streetlamps. I should be able to tell tomorrow night when I'm coming down from the mountain, especially with the high beams.
I really need to do this on my Camaro as I have a hard time seeing beyond the end of the hood. I bet I'd really notice with my externally regulated alternator.
PS. go to your local import speed shop. They'll probably have this same kit which uses 30 amp/5 pin/Bosch relays. I got both of mine for $9 each.
1968 C10 SWB Torch Red
1968 Camaro, 250\Powerglide, all original (No, I'm not gonna drop a 350 in it!....Jeez!)