Things haven't gone very well for sincerity on the comics page for the last few decades. Reasons for this range from the changing tastes of audiences and creators, the difficulty of selling a gag without a measure of sarcasm, etc, but I'd imagine it also has a little to do with how few current examples occupy today's comic page, making such attempts seem antiquated. There's real risk in the approach that Nancy takes every day, since absent the comforting distance afforded by ironic detachment, the strip has to stand on its inherent strength to resonate.
I think that comics need to have a level of dignity to them in order to function at all. If Nancy had fumbled into a more cynical mode to suit modern appetites, it would no longer be Nancy, it'd be hollow and mean, because the world in which it exists wasn't constructed for such purposes. Basically, Nancy, and the good folks around her are nice, and it's a credit to the integrity of the strip's architecture that they have stayed nice for so long.
In Nancy, the standard conflict you'll see will fall along the lines of "Nancy hopes to enjoy cake before dinner, even though she's not supposed to" and the resolution will either be that Nancy gets some cake and suffers a gentle, comic consequence, or Nancy doesn't get any cake and has to settle for having some cake at some later date. No matter what, she either learns or affirms a lesson, so there's no real "victim." See? Nice!
The enormous upside to taking a sincere, direct approach in a daily comic strip is that things in Nancy are able to achieve a level of delightful weirdness, in both contrast to surrounding comics and as an extension of its own tendencies, which simply can't exist in an environment where every character is built around a nougaty core of snark. I've taken the liberty of magnifying the weirdness by separating the following panels from their context, unmooring them from their less-weird setups. The more cynical among you might think that the preceding paragraphs serve only to justify my posting all the crazy stuff below. I truly pity you.
Props to Guy Gilchrist for keeping the spirit of Nancy alive and well. Things aren't always so weird, but it happens often enough to warrant checking out the strip regularly. But you don't have to take my word for it-- click here to see what you've been missing.
(Prove me wrong, readers. Prove me wrong.)