it's possible not messing up ore gen with Mystcraft, by rewriting some CoFH world gen config from whitelists to blacklists (for overworld ores, like copper, tin, and such, blacklisting Galacticraft dimensions...), so any number of Mystcraft world can be used as overworld, without making it too OP.
the useful feature of Mystcraft would be the ability of teleporting visited locations easily. but it would reduce the need of making ships and fuel, because once you get to Mars, you could make linking books and forget them.
the Warp book mod with pretty hard recipes could be a solution for teleportation (end-game stuff like the angel rings)