Use your Hearts of Ice. The entire point of Hearts of Ice is to help you narrow down your targeted prizes so you may get the better chances of winning something you desire.
Use your judgement on when to use your key. The entire point of using your judgement is to make sure you have the best strategy for using your TH keys on. Smart people can use commonsense, knowledge of TH, on top of Hearts of Ice among other TH tools to get the most out of any all kinds of games-of-chance, not just TH.
If you want just xp lamps and stars, just use your free daily keys and save up everything else you either buy or earn from playing the game for xp items on promotions such as Super Nova, etc.