I think we all enjoy discovering new techniques, and when we find one that yields great results we love to use it again and again. It's especially easy to do with watercolors because that adaptive medium lends itself to so many innovative paint applications. Personally, I'm in love with the palette knife--I can find so many ways to use it to add texture to my oil paint.
Awhile back, though, someone said that my reliance on palette knife work had reached the point of being a gimmick. What?! Me?! Gimmicky?! I was mortified to think that my work was becoming cliche. I immediately stopped using the tool I loved, and pushed myself to explore other techniques.
Recently, however, I picked up my beloved palette knife once again, only with a new depth of meaning. Without going into a lot of detail, I feel that this tool and the ways I'm using it actually contribute to the content and message of my paintings. The technique has purpose beyond making the surface look more interesting. And that, I've decided, is what will keep any technique from becoming a gimmick.