I know what you mean about undervaluing your voice. I was lucky enough to be able to go to the local college when I was 16 and have free singing lessons as part of my music course. It took me six months of lessons before I realised that my voice truely was an 'instrument'.
I consider myself to be lucky to have been born with such a good strong voice, but I know how much work I have put into it too. The only reason my voice sounds the way it does is because I made it that way. Just the same as an instrumentalist works on their intrument to perfect their playing, I have to practice and sing every day to make my voice something to be proud of.
I 'know' I'm a musician in the same way I know I'm.... well.... *tries to think of an example*...... *can't think of one*..... well I just know, alright! If you cut me in half you find the word 'Musician' inscribed... as well as 'mother', 'lover', dress-maker' and all the others. And some blood and guts an stuff.... better stop the analogy there really :)
*Hugs*
Catlin