> It got to the point, where even my rough sketches would be as good as finished works.
Hah, I feel like I understand more where you're coming from with that. I was the opposite, seeking to get my finished works to feel more like my rough sketches.
> I never really warmed to Boris Valleho's work (he used to hang in a gallery that I had work in, and I met him), but I have to admit, that guy can draw.
That he can draw is undeniable indeed. There are a few artists whose sketch work reaches that level of refinement almost immediately. Others get there after years of study and practice. Still others don't see that at as a goal at all for that stage of their process, and others still would see it as an antithesis to what they're after. Looking at Valleho's finished work, I can at least understand how his sketches are in service to that sort of end state.
Compare, perhaps, to some Rennaisance-era sketches. Typically far rougher compared to the finished works, but hardly less impressive. I'd suggest there's a great difference in what they were interested in: matters of anatomy, gesture, and composition. Of course, they were also inventing and rediscovering knowledge that modern artists have far easier access to. There's an interesting dichotomy in that some destroyed their sketch work, while others had far less interest in actually finishing anything.
I've forgotten an appalling degree of art history, so I can't readily name names, but as far as finished works go, I had a fondness for painters using relatively minimalist brush strokes, with each application of paint exactly the right color in exactly the right place.