Good discussion. Backwoodsman has clearly defined the slight bellying. I call that normal and desirable since I am a player. I use medium gauge d'addario or elixer nano phosphor bronze strings on my Gallagher Doc Watson. The tone and volume is what I want. Don Gallagher builds them for these. Now, if you are a collector, or wish longevity instead of a particular tone, then the stress on the top and bridge are less with lighter strings and MAY increase it's life without repair to the bridge or top.

What do you want? It's a clearly subjective question.

What you might be more concerned with is maintenance. For example, when I change my strings I wax my neck with butchers (bowling alley) wax to help prevent shrinkage which can cause cracks near the neck on the top. Are you taking steps to properly hydrate your guitar? Are you keeping a good coat of polish on your guitar?
A D28v can be a very good guitar, best of luck.
chance