Matt, you've made my day. This is one of my favorite kinds of questions! You are absolutely right that discarded starter will have less sugar in it than fresh flour, and that you'll generally want to make sure to have some fresh flour in your baked goods as well as starter. When making naturally leavened sourdough, the rule is that you want no more than 1/3 of your flour to come from your starter, and this is a good rule to live by when baking with discards as well. This is related to the structural changes that flour undergoes when it's fermented, the sugar issue as you've mentioned, but also because making rolls with all liquid starter would give you a "dough" (more of a batter, really) with a hydration of 100%. You'd have better luck simply pouring that dough into muffin tins and baking that way than trying to shape it into rolls in any kind of traditional fashion. Happy baking!

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