It feels good to be back to these forums after a year and I'll chip in my two cents.
There is no right or wrong answer to your question but for me personally learning music theory expanded my creativity tenfold as it allows you to have a foundation on which to start on and an understanding of why trying certain chords/notes/keys/progressions sound the way they do.
Let me try to give a VERY vague idea of how music theory improved my creativity.
When starting to look into music theory I began by learning about the major scale and in particular the C major scale as it is considered the "easiest" of the keys to understand because on a keyboard it consists of nothing but the white keys.
We learn that the C major scale consists of the notes:
and from here we can already begin to compose a song.
If I want to compose in the key of C I could select the notes C,F,G to create a chord progression (I,IV,V) and then create a melody or solo line over that using only the notes from the C major scale and for the most part (there are exceptions) it will sound pleasant on the ear and like it "fits" in that place.
If the next step was to learn about minor scale and the use of pentatonic scales then we would discover that the relative minor (a scale that consists of the same notes as its major counterpoint but beginning on a different note) of C major scale is A minor.
Because I don't want to ramble on forever I'll skip forward a bit and we discover that the A pentatonic minor scale consists of the notes:
These are the same notes that are in the C major scale (no sharps or flats) and like before we could choose the notes A,D,E for a progression and solo over it using only the notes from this A minor pentatonic scale and things will sound pleasant again.
At this point the argument comes into place that knowing this theory has hindered my creativity because rather than using my ears and trying new things (random notes?) I'm afraid to stray from the particular set of notes in the C major scale because that is "the rules".
It is at this point where continuous study of music theory begins to encourage and push your creativity. As we delve further into music theory and learn about scales other than the commonly known major and minor scales that provide us the ability to add new emotions to our songs.
If I take the A blues scale for example which consists of the notes:
we can already see that it contains a note (Eb) that does not "belong" to the C major or A minor scale that had been presented earlier. What's interesting though is that if I was to play the same A,D,E progression from before but now solo over the progression using the A blues scale instead of the A pentatonic minor I will discover that the Eb note is creating this strange and yet beautiful/mournful "clash" with the A minor chord progression.
IâEUTMve rambled on here and yet been incredibly vague in general, but this is only the very beginning of understanding enough music theory that I really believe encourages your creativity and lets you know why you can use certain notes from outside a particular key to create vivid emotions in your music. IâEUTMm of the belief that if you are serious about a particular field of music then why wouldnâEUTMt you want to learn absolutely every possible thing you could about it whether that includes sight reading, theory, improvisation and composing to any technical processes.