I don't think there's anything wrong with fooling around with "aspirational" pieces, meaning things you love and hope to be able to play someday. But I wouldn't do too much of it. I spent a lot of time working on things above my level when I was beginning, and I ended up playing with a lot of tension and very poor tone. I made much, much more progress when I learned to enjoy fussing about how to position my hands in the most perfect, relaxed way and play a single line with good tone and good shaping of the phrases. Even now that I've worked up to some fairly difficult repertoire I still sometimes take a whole practice day or at least an hour or so to figure out how to play a single line in one hand in the most efficient and beautiful way. There's lots of very beautiful music without too many notes. Working on playing simple things beautifully will improve your technique in the long run more than struggling with stuff above your level. Like I said, that doesn't mean you can't fool around with your "dream" pieces, too, but spending most of your time on them isn't the fastest route to being able to play them well one day.