At What Point is the Needle Damaging Records?

Ask yourself which is less expensive, replacing your cartridge or replacing your record collection. I think you know the answer. You asked if you might damage your records by not replacing the cartridge now. You described the sound you are beginning to hear. Do you really need a second opinion?

That's about $00.09 a day, not bad. Buy a new cartridge.

That's quite a few hours, I agree you may need a replacement. As mentioned check your set-up and try this cheap method to clean it; http://www.high-endaudio.com/Magic.html

According to Neil Young, he's seen the needle and the damage done, a little part of it in everyone. :-)

I would replace or retip it.

Ballpark is 1000 hours I believe. Your way over that average. It probably will be different with every setup. Tracking distortion happens in a lot of cases. Sometimes, it will show up more in the inner most track. It has been said if you have damaged grooves from one shape of stylus, using a different type of stylus shape may still sound ok as it will ride higher or lower that the damaged part of the grooves.