1) - Upgrade Replayability
After a certain point of grinding the same level over and over the game is inevitably going to get boring, and so people leave. Making the game more re-playable, such as by adding a bit of randomization into levels will stop people from leaving. Adding a new game mode will also help. I don't know the figures but i'll take a guess and assume that when raid was introduced popularity went up. Adding a different new mode, possibly with randomization will probably have the same effect.
2) - Revive pvp and bvb
Some good ideas about pvp/bvb already listed, anything that will expand the pvp/bvb playbase would improve the game. After all, if randomization makes the game less boring, every pvp/bvb game is different.
3) - Most importantly - Bot-Stract
The change of bot-stract into something else was necessary at the time, but as fuel it is completely useless. You said above you do not want to give coins/gigas as prizes, so why try and find a way to give alternative prizes when BC already has a 3rd currency embedded. BC/BOTS used to work fine with a tri-currency system, it makes the market more interesting and allows for many things, as shown by other suggestions.My idea was to use bot-stract as a currency to buy cosmetic items in a separate cosmetic shop. There are plenty of ideas already about how to gain bot-stract, while also increasing pvp/bvb activity.
4) - Community Input on Staff
Maybe this should go in the other thread, but i'll leave it here. Personally I think the playerbase has been negatively affected by certain staff members who the majority of the community dislike. While staff are there to enforce set rules, I think their main priority should be to help and be friendly to the new members. Therefore, I suggest that the community has an input on staff members, such as a thread where they can express their opinions from a list of choices. This means that the community would be more comfortable with the staff chosen and enhances the whole 'community' feel of the game.