Flavor improvement

It depends on the recipe.

It depends on _how_ you do the poolish, biga, etc.

It depends on what flavors or types of flavors that you seek.

Bon appétit, mi amigo.

Well they are different.  I tried a dry pre-ferment a couple of times, I got a flavour that had more acetic tones than I like, whereas a wet one results in a flavour I prefer.  But (and as a result) I haven't tried too hard with dry pre-ferments, maybe if I did I would be able to change things.

Starter maintenance-affects flavor as you can favor lactic acid or acetic acid or even low acid.

Pre-ferment-same as starter. Cold pre-ferment, warm pre-ferment, long development, fast development, dry preferment like a biga or wet preferment.

Type of flour used in any stage (wheat,rye,AP, other) , fresh milled vs commercial milled,

Type of bulk fermentation, any retarding?

There are so many ways to make bread with great flavor. What ingredients do you want to work with, what tools do you want to work with and what kind of effort or experience do you want to have making the bread? I learned how to make and maintain a starter that I like. Then I worked on making a daily bread. After trying many methods, I settled on the easiest one for me-natural levain, preferment, overnight retard,shape and bake. If I want a quick loaf, I may go with a straight through (esp if my starter is particularly vigorous)-mix,knead,bulk ferment,proof,bake. Still delicious but may not have the nuances of flavor. Occasionally, if I've neglected my starter and I want to bake NOW, I will use commercial yeast and get a great loaf.I've made my best 100% WW loaves using either an overnight cool biga  (Peter Reinhart) using commercial yeast or a liquid preferment and an overnight cold bulk fermentation using natural levain. 

All roads lead to........good bread.

It is definitely possible to employ all these preferments including sourdough starter in one loaf, the best of all worlds so to speak. Good luck!