I have some ideas of how to solve SK's main problem of falling player count. Currently, asking SK to implement things like different maps, increased spawn rate of certain enemies, more costumes, weapons, etc., is like asking a college student to donate to charity. Useless.
Here are some ideas I have that GH can do to increase popularity:
1) Reward players for sharing SK on facebook/twitter, etc.
2) Make a useful reward for players inviting friends to play, like 100 rads, not some confetti or similar
3) Provide mist energy for players with under X amount of hours/progress logged into the game. This would cushion the monotonous grind that occurs early on.
4) Offer login bonuses to help retain players
5) Keep up the regular events
6) Offer radiant/reward packages for reaching a certain amount of prestige
Login rewards would only interest me if they had ok rewards.... Something like this:
Common:
> 1000-10000 CR .
> 1-3 Spark of life . Max amount is very rare. Most of the time its gonna be ~ 2000cr or 1 spark.
Uncommon:
> 1-3 Alchemy orbs. Rank slightly affects Orb type.
> CR booster ( x1.5 or x2 ) Lasts 1 hr. Instantly activates when received. Its a trap card. If you log in and this drops...you just HAVE TO PLAY.
Rare:
> Silver key.
As for 2 and 6....I think it would be best to just fix damned rad droptables. Its a known issue. Grind for Rads is massive.