I'm looking to get back into playing piano after a couple of years hiatus. I can still read music sheets pretty well with the occasional ledger line throwing me off but, I don't have much knowledge in terms of music theory.
So far, I've just been finding sheets to songs that I enjoy and playing them. Is this enough or should I be studying things like music theory alongside playing songs I enjoy?
Short answer - yes, learn some music theory. It can only help.
Longer answer - from what you've written, "I've just been finding sheets to songs that I enjoy and playing them...", it seems that you are learning pieces through a combination of reading as well as "by ear". You know how the song "should sound", and you are learning the notes visually.
But what if you wanted to play a piece you had never heard?
In that case, you would be reading the notes, one at a time, playing them at the keyboard, but you wouldn't have the context of knowing the sense of the tune.
IMO there is an valid analogy between reading music without knowledge of music theory and sounding out words in a foreign language by reading them phonetically. Reading and playing that way we might get the musical words stated, but without knowing the context, i.e., without knowing how they fit together, our performance would be mechanical and, ultimately, unmusical.
Learning some music theory - scales, chords, understanding how harmonic tension is built through leading tones - these are things that will not only make it easier to play new songs. They will also help play those songs more musically.