I generally attribute "soul" to items that may be arguably lacking, outdated, or nostalgic in nature. I like the look of wood and steel. I am really close to picking up a SA Loaded because of that. I find the 1911 oozes soul. It also weighs 40oz, holds less than half of a similar sized 9mm, and at times can be a bit picky with ammo (some of them. Not a blanket statement).
I've got a covertable Blackhawk I'll never part with and a 12 gauge pump sporting walnut is the granddaddy of a utility based firearm looking good doing it.
That said, if it's made out of plastic I just don't feel the need to attach "soul" to the gun. I've got an FN 509 by my bed and a full size P320 in the next room. Neither are what I would call heirlooms or soulful. However, they are the first line of defensive arms I had at the ready to protect my family as my long arms are stored more securely. I find a brutal amd cold beauty in their design. Strip out the heart and replace it with steely purpose. I find a warm comfort in knowing they will do their job if I do mine.
I even feel thw same way about my pocket guns. The BG380 in my pocket has no soul to it. One of a million+. Black on black and completely stock short of the dab of paint on the front sight. However, what it lacks in personality, it makes up for in loyalty and readiness. See, that dab of paint on the front sight is a bit of nail polish that my 8 year old made. Its coral orange and works, plus it reminds me of why I carry: To protect and/or get home to my family. The gun itself is boring. However, I do take comfort with it in my pocket. I like the feel of its rough polymer when I put my hand in my pocket.
Almost none of my guns have what anyone would call soul. But they function like the reliable tools they are.