Since you don't care about the rewards anymore, try making your own challenges just for the fun of it. After all, it doesn't matter to you much atm about xp per hour or cash, so why not try playing some of the minigames that don't necessarily have good rewards etc. Make a list of everything you think to do on RS, and then do the list. Things like "Solo every boss", "Catch a Big Shark", "Get a chompy hat", etc. etc. A lot of the fun things to do on RS aren't too rewarding, but that doesn't matter to you, so you're free to go about doing whatever you want.