So right now my game doesn't use textures at all, only vertex colors. However many things would benefit greatly from texturing (e.g. vegetation, clothing). Adding textures means

1. Higher engine complexity
2. Much higher content creation cost

(2) is my major concern.

Anybody got any opinions/advice on this?

@lisyarus I like the vibe you have going textureless. If you desperately need detail in your models you could always add additional triangles and continue using vertex colours (which I can see you've already been doing in your screenshots).
@jargon Thanks! Yep, I've been working on higher triangle density, and tbh at this point I'm seriously concerned with performance, there are just way too many triangles. Decoupling triangles from detail density sounds so tempting!
@lisyarus @jargon maybe you could create textures that make it appear as vertex colors. You'd get the same look, but won't have to increase number of triangles to get more texture detail.