I am still finding the PoE well worth the time without keys, personally. You get the vanguard rep and marks, strange coins and motes from the small chests. The small chests also drops mats and can drop keys themselves (I got one from a small chest last week and then immediately used it on the big chest, got an exotic!). Also as I commented below you still get two item rolls in the post game screen that can award legendaries or exotics. I've gotten multiple legendary queens weapons from the roll at the end and an exotic (The Last Word). The key just greatly increases the odds of getting something awesome (got my first Gally from my first key!) but you can still get plenty of bang for your buck running it without one.