The current system of Alliance advertisements is not very good because:
-Imagine yourself sitting inside your own citadel in your sovereign space and then you see the alliance ad of your worst enemy alliance on a station billboard. And your alliance new recruits see those every day.
-Since the introduction of these alliance ads the number of ads playing on billboards grew significantly. This means to much noise around important information you might looking for. And if you simply want to watch a particular ad again you will need to wait for it for forever.
How do you improve this particular part of the game? I propose:
Make alliances (and corps with ads) buy the permission to display their ads inside of a station or citadel. This system might work just like corporation offices. The price inside NPC stations might be based on regular player population (just like offices) and it will make a nice ISK sink. Alternatively you can make alliances buy permission to place their ads on all stations of particular NPC corporation or maybe even the whole NPC empire. The price in citadels is obviously will be player driven and will generate some nice profit for citadel owners.
Such feature will allow some alliances to perform recruiting in particular areas, and to get rid of hostile ads from their own citadels. It also will unclutter billboards as there will generally be lesser number of ads. And last but not the least: new isk sink.