Ah, I see the point you have about doing a 'First year' chart. I'm probably going to do a guessing one at the end of the year too, though, just for kicks lol. At the very least, I think I know what's going to chart #1 on my 2010 year-end chart.
I definitely see how inverse points doesn't work too -- I myself have gone through my music and noticed something that's never reached #1 even though it's one of my favorite songs, merely because there might've been a really good song that charted that week too, so the exact numbers are a little too inconsistent to use as a basis for a points system.
I'm interested to hear how you've helped remedy that. The only thing I can think of is giving each week a value and multiplying each score for that week by that number -- like, if you really enjoyed music a certain week and listened to a ton of it, give it a "2", or if you didn't listen to much at all, giving it a ".5". Which, come to think of it, is actually a fairly interesting way to approach it, albeit it requires lots of math lol.