What do you think @winemaker81 ?
I've been married for 30 years, so I learned to not think, as it gets me in trouble every time!
Sugar only is going to increase alcohol, which improves shelf life and mouth feel, to some extent. Concentrate does that, plus provides more body and flavor.
The Island Mist wines I chaptalized (sugar only) were fine as they were, as they met my expectations. I wasn't looking for a complex wine -- fruit flavor and complex red/white aren't 2 things I'd put together.
If looking for a deeper wine, add concentrate. Personally, if I was adding concentrate to an Island Mist, I'd add enough sugar to bump the ABV to 11%-12%, so LP's advice of 1 lb sugar is too low IMO. If the body increases, aging time will as well -- but if the wine is below 10% ABV, it will have a shorter shelf life. I am concerned that such a wine would age oddly -- I have no proof of that, but knowing how wine ages makes me suspect it.
I have plans for fruit wines this winter, and am strongly considering buying an inexpensive red kit for the concentrate, which is a total of $8 USD per liter. Whatever I don't use, I'll freeze for another use.