Rob, For years I believed the same as you that I couldn't write music. I still can't technically - that is put the dots on the paper - I record my tunes by singing them or playing them onto a minidisc. Don't dismiss it as a mad idea, I finally gave it a go 2 years ago, last year I came fifth in the Plymouth Folk Festival songwriting comp and this year I won! Why not have a go yourself, perhaps you'll surprise yourself, like I did!
GOOD LUCK!
Cheers, Lucy