you don't feel all different just cos you ate an apple (apart from the nutritive value)... it's got MALIC acid in it that must do something shorely
ahem
the thing about the other salts only would make any difference, maybe, if you were injecting, as the acid ions have some effects when they are introduced directly into blood (as an example, HCl concentrations cause elevation of body temperature, some salts can cause strange sensations when injected but this kind of condition is rapidly fixed in the blood via buffers and other mechanisms)
The burn you are talking about from snorting is very likely from over-acidified speed, or you aren't powdering it finely enough. Try making a solution of it sometime and get one of those blow spray things (one tube blowing across another at right angles) and get a friend to blow the solution up your nose, of course use the minimum of water, hell it doesn't matter if it's a little warm even. Or put into a nasal sprayer...
the other vaguely possible source of the burning might be from residual sodium chloride that can form if one does not wash the nonpolar extract of the freebase properly when extracting it. Salt does burn membranes. It is actually acidic as well, it's pKa is 6.5 (that's the pH a saturated solution of pure sodium chloride would read). The alkaloids, while they are alkaline, are much weaker bases, in fact weaker than sodium bicarbonate, i don't believe they are that irritating to membranes, certainly not compared with salt or occluded water in the crystals containing HCl.