There is a lot of talk in the faq about looking for foam and bubbles
and so on in deciding when the dough is ready for the next stage. I
use a firm whole wheat starter and bake 100% whole wheat bread, so
there's no foam; since I can't easily see how many bubbles there are, I
tend to use odor as my indicator.

The dough goes from a distinct "wheat germ" smell at the beginning to a
"fruity" / "champagney" smell after some time, then, when optimally
ready for the next build, the dough gets a distinctly "sour" odor.
Ironically, this last one is the least aesthetic of all the odors; it
can at times even smell a bit "off". But that's when the dough is
filled with air and light and ready for the next build. It doesn't
taste sour, mind you, just smells that way.

I've noticed my white and rye starters tend to go through roughly the
same progression (alcoholly, then sour) but obviously don't smell of
germ at the beginning. I've noticed the same progression when using a
liquid or firm starter and dough as well.
Anyone use odor as an indicator? If so what guideposts do you use?