For a long time, I felt like I should play every day, even when I really didn't want to. And while playing every day does enhance my muscle memory, I've found that playing every day sometimes does more harm than good, for me anyway. If I work on just one song, or arrangement, day after day, I soon grow tired of it, maybe even start to hate it. So, I usually have 5 or 6 that I work on. Even with that diversity, I find that I run into a sort of brick wall sometimes, where a tune just doesn't flow like I want it to, or there's a place where I struggle, and I might give up in frustration.
Now, before I hit any rough patches, I just walk by the piano, maybe go outside, take in some nature, or whatever. Then, I pick one of those tunes I'm working on and play it in my head; not thinking about the notation, or the fingering, or anything technical. I play the song in my head the way I want it to sound, as if I were listening to a recording of it, over and over. After a day, or two, or three, or even longer, when I sit down to play it again, all of those rough spots have vanished. It's like my subconscious knows how the tune is supposed to sound, so my fingers seem to have an easier time making it sound the way I want it to sound. So, that's my method of madness for practicing the piano.