IMHO, the question how Russia would feel about the Danubian principalities or territorial gains in the Caucasus (it would feel good) is not as relevant as the question who would give then to Russia as a reward? Not to imply that the Turks were (or are) the excessively stingy people but giving big chunks of their territory to anybody as a gift (aka, without putting a good fight) would be probably too much to expect.
Serbia belongs to the same category and has an additional disadvantage of being on the wrong side of the Balkans.
The only valuable place close to the "northern part of Sweden-Norway" is, AFAIK, Petsamo but it was already in the Russian hands and its value became clear only in 1921 when the big deposits of nickel had been discovered there.
As for the Baltic islands, if one removes from the picture the islands that Russia already possessed, there was, actually, an interesting option that would not fit into a category "My armies went all the way to Paris and the only thing that I got is that lousy island". How about Russia getting the following islands (from a former Napoleon's ally): Zealand, Funen
, Bornholm
, Falster, Lolland, Mon, Læsø, Samsø and the smaller ones in between?