Nether portals are not allowed in Mystcraft dimensions anyway. You cannot light one, and the only way to get one is to cheat a portal block (since it would be a super easy way around getting lost ala Myst/Sliders). I don't know anything for sure about IC2/GT teleporters; seems like I read something based on the presumption a teleporter could send things between dimensions.
Q-Craft inter-server does allow togglable and presumably unbeatable restrictions on whole inventory transport (it's not a tesseractable dimension... it's a whole different minecraftforge jar instance). I don't know if it would be possible to restrictively allow only certain items to move through. Another mod (endernet, I believe) does allow item transport between servers with pipes and such (but I don't know in what ways items can be whitelisted or blacklisted). Q-Craft doesn't have to affect anything on the server except to enable such a portal, really, if you were to disable its oregen. ---I don't know what would happen if you tried to log onto both servers simultaneously, or if there is a way to make the logins mutually exclusive.
As to Mars PvP: What happens in another planetary system, stays in another planetary system. Also... if two consenting adults participate in something and can be adults when someone comes off worse, I don't see why an admin would stop it in any dimension.
While I set all sorts of silly rules for myself, I do agree with BA's statement that a server economy will always operate in the most economical way, and artificial, morally-motivated bubbles will always be fragile especially if there are anarchists afoot.
I still propose a mid-term tick-lag-test with Thaumcraft alongside the rest of the basic mods proposed. It may not even be viable at all, rendering this whole debate moot.