Sorry for being a bit late on coming into the Vong conversation but i'd like to start it back up if you all wouldn't mind. Or at least put in my input towards it. The majority of smaller factions aren't going to get new people, it's just not going to happen. Especially very new people who may or may not know as much about star wars as some of the fanatics of the community. (Such as myself, so it's not a dig.) Which means that they're going to do one of two things. Join the Jedi or Join the Sith. Because it's in the movies and they know what it is, they have absolutely no clue what an Echani is or what a Yuuzhan Vong is; however, the majority of the smaller faction members are going to come from either members within the community or people who know the Star Wars universe a bit better have roleplayed on other Star Wars sites and wish to not transfer their characters.
That being said, an example of how the Vong could amass a lot of people to its side is of course utter domination. Just like the canon Vong came in an annihilated super powers of the galaxy such as the New Republic. So much of posting and writing in a roleplay like this isn't even how long your empire has been around or how long you have been around. Granted it helps, but it's not all of it. If you've been around for years and your writing is lack luster and sub-par, yet you face a brilliant writer who just came into the community a few months ago, nine-times out of ten in something as even as a space battle they're going to destroy you and dominate you. Writing is an art from the way you portray yourself to the way you portray your characters, and how you can dominate others through writing. The major thing here though is that if a Minor faction wants to get people to come into its folds it needs to make big moves across the galaxy. People want to be on the winning side of things, they want to be able to dominate other players and other characters to allow their character to reign supreme. (It's human nature, and the human condition.) Also making these big moves across the galaxy provides roleplay for people, and what to roleplayers love best? Roleplay. People of the community may be magnetized to roleplay if they see a lot of it.