Stainless being soft has to do with the specific alloy. Some are quite brittle.
It's usually a little worse at conducting than normal steels.
I think galvanized might also have a wee touch of resistance.
The question is does the benefit of less corrosion outweigh the small difference between metallurgies resistance over time ? Cost a factor? Obviously it does matter for some folks; but why? Usually because they are outside or in a very damp area, or the have a rust or oil phobia, etc..
Brass also comes in various grades, from noodle soft to brittle. Good conductors and doesn't rust. I really like this thought of brass pins. the work hardening part isn't even scary as you could drill out brass and leave steel intact if needed. Copper is too soft. Aluminum has a lot of resistance potential compared to steel or brass. It corrodes funny, breaks easy, and....and I just don't like it for electrical period.
The only part about some modern nails that I worry about is they can be surface hardened pot metal steel not fit for anything structural. (glorified slag) . I guess you could open and close the web if one broke though.)
Hey, cut those wrecked ends off after you slide the tie back more, and make custom pieces from them as needed. Reforming around a pin is pretty easy with dulled top cutters or similar pliers. Just bend/wiggle the closed web a tad left to right then centered and it will stay closed again; then fix the foot halves or oblong or stake the tube to get real tight. (Spinning pins are not tight enough. Pressure greatly reduces resistance in connections.
I don't think that softness matters too much. Marx pins are very soft. The softness actually seems to grip better. They are definitely an alloy. A low grade stainless maybe as they never rust. Maybe just a zinc alloy.
A related side note. I noticed a slowdown on a couple of pieces of very old track on my El. I recalled someone mentioned they regularly sprayed a tiny bit of the CRC contact cleaner on joints while cleaning track with it, and over time issues faded.
Sure enough, two small drops at each joint/pin and every slow down was eliminated without so much as a finger wiggle on a rail. It's been near a week without change, but I'll do it again soon anyhow; I have a new ritual in mantaining track from what I saw 
