They got "their hands dirty on actual politics and compromise" as (intially a minority) government in Scotland, and have continued to gain support ever since. I believe Alex Salmond was one of few political leaders ever to leave with a higher approval rating than when he started.

Apologies if you already knew that, but there's a lot of commentary about recently that seems utterly ignorant of those facts.

It's probably worth reflecting on your words here too: "never achieve anything, as they have exactly zero leverage to affect anything in Westminster". That's a double edged sword for people who want to keep the union together for the benefit of all.