I've been watching this topic since the beginning and I didn't have much to offer except that sugar like salt is too bad, so sad when you add too much. You are seldom able to correct your mistake except next time you cook it, or making a second batch and mixing them. That is still my feeling. You can to some degree add sugar to counteract the acid in tomatoes (so I'm told and that is my experience) but I've never seen any way to counteract too much sugar, even by adding acid. Nor salt; once too salty the only recourse is double recipe and no salt to the second batch you mix in.
I'm reminded of Lady Bird Johnson's "Pedernales River Chili" recipe
. There's no sugar there. The lesson is that seasoning should be reserved until the final stages, until you can taste the cooked or almost cooked ingredients. Perhaps you've added 1/4 or 1/2 of the recipe amounts of salt, sugar or other spices. That's the time when you "season to taste."
I really like Jolokia's suggestions to add sweet fruit to achieve sweetness for those who want sweeter chili. I think it would be really productive to add mangoes. Particularly if you have added onions, and I have no reason why I suggest the mango/onion combination except perhaps intuition plus my liking chutney. Chutney is also a combination of spiciness and sweetness. Perhaps that's my inspiration.
p.s. I too would not add chili sauce or ketchup to chili. Get the tomato taste from whole tomatoes, canned if you want. And also, noting, masa harina is the perfect thickener for chili. I don't know why but it is.