I've got this friend named Mark Eshenbaugh who builds absolutely gorgeous basses: http://www.eshenbaughguitars.com/
I was talking to him recently about all the different factors that affect tone. One of the things he mentioned was frets. Dirty, tarnished frets are not conducive to good, clear tone.
So, I used some of the stuff he recommended: http://www.stewmac.com/cgi-bin/hazel...shing&sku=3518
I masked off the fretboard with tape and went at the frets. You wouldn't believe the black gunk coming off those things.
And when I was done and polished them up - the change was remarkable. Those frets SPARKLED!!!
I got strings back on it this morning and played for a few minutes before going to work. Maybe it's all in my head but everything just seemed a shade smoother. The neck felt faster and the sound was clearer.