Even removing alcohol from the picture, the ingredients in the pot are not as static as you might think. For every moment your sauce is being reduced maillard and other flavor compounds are being created as well as boiling off. At least from a stock perspective. My observation of stock has been far great than wine. If there is caramelization of the sugars in the wine occuring, it's not something I've studied. Looking at it from strictly a stock perspective, though, anything that prolongs the reduction, either by the addition of extra water or a lower temperature, will change the nature of the final product. Depending on how much water or how much one decreases the temp the difference can be quite dramatic. I personally find long/low temperature reductions to impact stocks negatively but, as with everything in the stockmaking world, there are those that feel the opposite. Will the extra duration caused by the equivalent of 1/4 bottle's worth of water make that much of difference? For me, I would say yes. I go to great lengths to limit the reduction times for stock. For someone else, though, the impact may not be that discernable.