It is certainly a good idea to age sweetened wine. How long, is a different question completely. I point to one of the first wines I made, actually two wines. Both peach, but made using two different recipes. (It's going back about 10 years now and I don't recall the differences other than to say there were differences.) But I digress. After about 3 or 4 months, both of them were just kinda boring, nothing special, little peach taste. We finished drinking the bottles or so we thought. After about 3 years I found one last bottle of one of the wines. Opened it, expecting nothing special, boy were my wife and I surprised. The peach nose almost overwhelmed just at opening the bottle, the taste was wonderful, if you liked peach things. So you can age them, but like all wines there is a lifespan and what that lifespan is depends on the wine.
Also, when I make a sweetened wine, the last step I take is to add the sugar. I pull out three or four measured amounts, add various amounts of sugar to each, re-arrange the wines, then my wife and I, and hopefully some extras give a taste. We then decide which one we like the best, mix up a bit more and let it sit overnight and decide if we still like it. We also try to use a bit less sugar than we calculate. With aging (unless you invert the sugar) it will get sweeter with time.