I've noticed in one of my games (PBW, 1.67, TDM-ModPack, 2 human players), many of the planets I'm creating have values of far more than 200 % per ressource type.
Is this a bug or a feature?
It's a feature. A recent patch added new settings for asteroids to have very high resource values. This makes remote mining actually profitable and then makes the planets created from asteroids very valuable.