What Makes For a Good Tomato Soup vs Tomato Sauce Recipe?

[jjhunter]

I have a modified tomato basil soup recipe that I use for as a base for tomato sauce as well (whether the end result is for spaghetti or pizza sauce). The only difference is that for the former I also add in bouillon cubes + water + a dash of dairy product (cream or a spoonful of plain Greek yogurt). Naturally I've gotten into the habit of turning my homemade tomato sauce leftovers into homemade tomato soup, with varying degrees of success.

What makes for a really good tomato soup recipe versus a good tomato sauce recipe? And while I'm at it, what are other creative uses for leftover homemade tomato sauce?

ETA: I've written out the modified tomato basil soup/sauce recipe here in the comments.