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My own particular bugbear is with music scores. Why some composers write them with 5 flats or 5 sharps I know not, but I completely avoid such music. It's way too complicated for my old head to comprehend. I can play many many chords and read music, but my old music teacher I think had a point when he said that the more complicated the music was, the more the composer was trying to show off HIS expertise, whilst making it totally indecipherable to most players.
So enjoy whatever keyboard you have , and play it. the rest is theoretical.
Yes, it is possible that some composers are just showing off when using more complicated key signatures. But there could be other reasons. First of all, some key signatures, with their combinations of black and white keys, are just more comfortable to play in for certain songs. Think of the traditional blues scale -- typically C, D, Eb, F, F#, G, A, Bb, then C. Once you learn that scale and start doing blues improvs with it, it feels so natural that this scale in other keys just doesn't feel as fluid and natural -- at least, to me.
Secondly, a less often used key signature can make a song stand out, audibly. In a sea of songs played on the radio in keys such as C, F, or G, when something suddenly comes on in, say, Db (5 flats), it can create a sound that stands out on a subconscious level, even for people who are not musicians, because it doesn't just fit in the "matrix" of the more commonly used keys. In my experience, Vangelis likes the key of Db, which is the key that Chariots of Fire is written in.
