I found a "planet" that is only a Gateway. I spent the Core Fragments to activate it but all it did was bring me to the outpost. Do they eventually go somewhere else. If I find another besides the starting one will I be able to travel between them? It just kind of seems purposeless at the moment.
I may be wrong, but I believe they're a fail safe for joining multiplayer games. If you join a game in progress, you might not have spawned in the correct solar system and you might have been out of fuel, so they're there to get to the outpost if you can't get to a low threat level planet that would have a gate. This is speculation, however. It could be a remnant of the old system that was never removed, in which the gateways were the only way to get to the outpost after powering your ship's engines with core fragments. Now, gateways use core fragments directly.
As of version 1.1, after you complete the main storyline a merchant will appear on the balcony on the right of the outpost who will sell vault keys for various items. These vault keys can then be used at ancient gateways to enter "ancient vaults" - very difficult procedurally generated dungeons that allow you to obtain and use ancient essence to upgrade legendary weapons as well as a way to obtain terraformers and microformers.