I suggest you should continue to be able to level up past level 150. I also suggest that as a reward to everyone who gets to level 150 that they get a dragon, this would reward long time gamers, and I also suggest that every 50 levels after that your rewarded with a new dragon. So for example if you get to level 200 another dragon is given to you. This would also motivate people to play with community and neighbor islands because you get level up points for that.