This is one of the issues with working on each part separately, instead of working iteratively on the whole piece, since you're not relating the parts to the whole to the same extent.
you make some excellent points; although I don't think it's caused by working on single elements but rather that I tend to overrender whenever I try a new style for the first time (it's a bad habit). I have the same when I do work on the entire piece rather than small elements.
I was planning to give the entire piece ant overall pass near the end, so this will certainly help.
EDIT:
for clarification, when I talk about rendering in this context, I talk specifically about shadows and highlights. Not details. Even with lineart I cannot always control myself and forget the less is more route. As a result, I run a very real risk of turning my piece into a murky mess.
Knowing when to stop is a very important part of the sport, and whenever I experiment with new styles I tend to loose sight of that aspect. This is something that always gets better with practice, but having people point it out will certainly help me get there faster.