2 issues at play here. If you have hard water, you're likely to feel "soap scum" on your hair without the acidic rinse or something to get the mineral/soap residue off your hair. Citric acid in a product might do the trick if there is enough in there (and if the pH is 4.5 to 5, there must be a fair bit).
Vinegar does smell vinegary and can be itchy, especially if you've got a sensitive scalp or "mold" allergies.
I don't know if soap bars in soft water present any problem with residue.

As far as un-swelling the hair shaft after exposure to the high pH of the soap bar (and getting the cuticle to return to its normal position), your low-pH products are going to help with that so why bother with an extra step?