I have a very similar problem... I have only got one mod to work ever. and now anytime i have a mod installed, I never had population growth. Doesn't matter if its a custom map, a mod, or an asset.. Just builds and no one ever moves in.... very shitty. In addition none of the assets I load show up as buildable objects... In some cases, no matter if I remove the mods entirely and restart the game, when I create a new game, no population increase occurs... I had to uninstall the game, and start over for it to work again.
.... waiting for that patch that works... this includes the 1.0.7b patch that just dropped with notes that read : Fixes Mac assets.