It's amazing the things you find by accident isn't it!!! Most of the riffs I've written for my songs have come about as a result of just messing about on guitar...every now and then you'll play something that sounds good, and you'll want to keep it.
There are lots of ways to spice up a simple 3-chord progression - you can try adding sus2's, sus4ths, 6ths, 7ths and 9ths over your basic chord shape. You can alter the strumming pattern. You can substitute chords - try an Am7th instead of a C. Try minor or maj7ths instead of major chords.
There are a million permutations as yet undiscovered - I'm hoping to find a few of them myself. If you find a good one and can't use it, let me have it - I can always find a good home for a good riff!
Don't be afraid to experiment - that's the key. Another way to change things around is using different chord voicings. I was once told Paul Kossoff was trying to change to a G chord and misplaced his fingers - came up with the riff for "All Right Now" by accident. His head was thinking G as a half-barre chord, his fingers were somewhere else - and he hit this chord....xx5030 - it's a G6 chord without the third. He liked it so much he kept it in the song, and the rest is history!
By the way, I like your idea of keeping a record of amp/pedal settings - think I'll pinch that idea, if that's all right with you!
Vic