Adding to the sidquest idea: There should be common quests that give you more money, uncommon quests that give you extra work points and rare quests that give you more rubies.
I'd work on the credits per second coding. It seems you have it set to add credits every frame, not every second. If you used Unity to make this, take this out of the Update method and create a separate method and use invoke repeating for that method.
Well, "I" personally can't lol. XD