Why does the Silver Tribe pursue the Argonaut even at times when Age/Bellcross isn't on the ship? For example, when Age is fighting in the Cemetary Belt, and the Argonaut warps away, the Silver Tribe sends a whole bunch of Bronze Tribe and Silver Tribe vessels after them. Why?
Why not? Nothing they have can possibly stand against Bellcross except their own Nodos, and the Argonaut is a relatively powerful Iron Tribe warship. Might as well have their ships pursue it. If they stop it, could Age find his way back to humanity? Maybe, but maybe not. Also, if they stop it, it doesn't bring back word to the Iron Tribe that their Nodos has been found. Recall that it was Age's arrival that prompted humanity to begin a serious counteroffensive.
If the Silver Tribe can teleport anywhere and create matter with a thought, exactly what was stopping them from simply teleporting onto the Argonaut and massacring everyone inside?
Efficiency. Their full hedron ships can shoot down enemy ships much faster than a single Silver Tribesman could do from the inside. Also, recall that, for the most part, each full hedron contains one Silver Tribesman. That means, most likely, that there would be a single soldier, or a handful of soldiers, against the entire complement of the Argonaut. Hedron shields are not invincible. The tactic is just too dangerous to be worth it.
It's also possible that the tactic simply never occured to them. They are beings with considerable psychic abilities. Naturally, those abilities would be what they relied on in battle. Attacking from a distance behind lots of big hedron shields makes more sense to them than exposing yourself to great personal danger on an enemy battleship.