Denmark unifying Germany is like Bohemia unifying Germany. At least ethnically. Not that it mattered too much for the Danish kings since they already ruled over many Germans in Schleswig-Holstein.
If Denmark isn't unifying Germany (let's be honest, that's just Germany with some islands and Oresund), it can compensate by getting a huge chunk of northern Germany (i.e. doing really well during the 30YW), exploiting the Sound Dues for everything its worth, more activities in the Baltic (get back Estonia and Gotland or more?), and a bigger colonial empire. Grab some more sugar islands, get into the slave trade and stake a claim on a lot of Africa, more activities in India and maybe even the East Indies, etc.
Denmark also has the advantage of not having to deal with Russia next door as Sweden did, unless they go the Estonia route.