As far as I know, brown sugar is just cane sugar plus molasses. I'm thinking that this would be 100 percent (or nearly) fermentable. In that case, I believe you would actually get the higher ABV, but lower mouthfeel. Mouthfeel often comes from residual sugars that the yeast cannot ferment. In the case of brown sugar, since it would be more fermentables, the mouthfeel would get lower. I would say you would be better off using more extract to get what you are looking for.
Anyone else want to chime in on this one?
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