I know I'm not an admin, but I used to be, and hopefully this will still shed some light on your situation:
Back when Warriors Fanfiction Wiki (WFW) was founded, in 2008, it was created as sort of a "sister wiki" to Warriors Wiki (WW). The person who went through the process to create it was Eulalia459678, whom we now refer to as Eu. He and fellow admin GroceryBag, whom we now call GB, made this wiki specifically as a companion wiki to WW. For that reason, users from WW flocked to WFW as a place to be creative within the same community and to work under extremely similar rules (they were changed to fit the needs of a fanfiction wiki).
Over time, the two wikis have grown and flourished into their own completely separate communities. Erin Hunter has left a note on one of the admin's talk pages over there (it may have been Kate or Vicky specifically??) but has shown no attention toward us. That is one of many indicators that our wikis have changed. Now, as I write this in 2014, we don't notice many users floating back and forth, although I'm sure we have a few. It is difficult to maintain a presence on two wikis, especially if they are on the same topic.
There were two points in my wiki history where I decided to venture out and start trying to find other wikis. The first was Percy Jackson Fanfiction Wiki, which was run by a user called Sparrowsong (former admin of WFW). I eventually drifted away from this wiki, my home. I was a rollback at the time and one of the only reasons I returned was a desperate message from a user here (Arti, in fact) to help stop a vandal (I contacted an admin).
The second was when a user named Nightfern contacted me in a way similar to this one, asking me to form a partnership with her wiki, Warriors Share Wiki. I did, and eventually helped to start try and build their community of completely separate users. It was successful, and I eventually drifted back to this wiki. To this day there is almost no fluctuation between the users of Warriors Share Wiki and WFW.
There were a few other dramatic moments involving other wikis, including Join MoonClan wiki, Ragnor, and some user called Violetofen4 (who was from a wiki that I forgot the name of, I think it was Warriors Roleplay Wiki).
That whole thing being said, while a partnership can be promising, it can be very difficult for users to, in a sense, balance their time between two wikis. While it's easy in the real world to have multiple social circles, it's not so easy here, because your attention on the internet is only during the time you are there. For those of us who have 30-minute time limits on the computer every day, it gets even more difficult.
I'm not against a partnership, I just want to remind everyone that it is difficult and it often doesn't produce the same results that we had pictured in our minds. :)
Also, I'm not an admin.
Good luck with your wiki!