I completely agree: The travel-agent UI and (also, but less, the startport UI) are painful. Your idea of showing all the possible destination (maybe with lines to them) right away on the galaxy-map is what I've had myself for a while. Starports (where the galactic-liners arrive & depart are just like other sites at a space-station (I think they are square-white with a purple star on them).
Most of these UI things don't have high priority at the moment because I have a lot to do in the content area (ways to get better items, dialog, stories, etc.) and that's what I'm focusing on at the moment. I will add a button to quickly go to the planet-information panel of the planet you're on but this travel-agent/starport UI thing will probably have to wait. (I'll probably have a look and estimate how much time it will take. If it's not too messy I will do it soon).