I'd think adding sugar would increase the sweetness. By the way, the sauce I make (or at least, started making yesterday!) is pretty sweet. I just used Stanislaus Full Red sauce as a base (thank goodness I found a source for this yesterday), then added pizza seasoning, water (to make the sauce a little creamier, and also to dull down the strong taste of the sauce base a bit), and salt. No sugar. I did my first try yesterday, and it came out sweet and smooth.