Personally I leave it up the company actually selling the headphone to attempt to justify the price to myself as a consumer. Asking a Sennheiser fan for a headphone recommendation is a bit like asking a Justin Bieber fan for music recommendation. We all have our own preferences. It's entirely possible that for you the iPhone earbuds are an end game headphone that will make you happy for the rest of your life.
If you aren't left longing for higher sound quality by your current equipment don't go seeking high quality, because you will likely end up spending a bunch of money to simply go in circles for no reason at all.