My 520 is still shiny new, so I'll admit to vanity of maybe a 7 right now. It's an all-around bike for me (commuter, charity rides, club rides, etc), so I do take pride in how the bike looks. But I'm aiming for a 3.
However, this question made me think more about my own progression as a cyclist, in terms of vanity about myself and how I look on the bike. I started as a 3 just trying to keep up on my hybrid, then caught "Lance wannabe" fever after I bought a used Trek road bike and started collecting charity ride jerseys, and crept up as high as a 7, and am coming back down the scale again as I discover my "inner tourist." Cargo shorts over spandex, carrying the trunk bag on club rides, etc. Aiming for a 3 there as well.
Ken