a good mix of chords and notes that are too hard
I would think that anything that stretches your mind is useful. Chords you are unfamiliar with will just help you keep learning. Learning to change up between chords quickly and seeing the patterns in chords will certainly help you develop. Though, if you really want to improve it is always better to go for understanding over memorization. For instance, there's not just one E chord, there are several. Which one is useful could be different at any moment, depending on the tone you want or the position your fingers are in. Learning your musical alphabet and reading into music theory can help you develop much faster. It is a simple thing to take the standard E chord, move it one fret over, barre the first fret, giving you an F chord. Then again for an F sharp, and so on all the way up the neck. Music theory is a complex thing so I'd suggest starting on it now and coming back to it once and awhile, trying to understand a bit more each time. That all depends on your level of interest in guitar, but with enough fancy booklearnin' you can get to where you understand the mechanics of scales, chords, and chord progressions. Once you understand that then you don't need to memorize chords because you can just make your own!