At What Point is the Needle Damaging Records?

Get a loupe or magnifier and carefully examine the stylus. Sometimes you'll find dirt is the issue. A layer of grunge may have built up that does not come off with normal light brushing.

It may be difficult for an untrained eye to spot mild wear, but it's still a pretty good habit to visually check the stylus periodically.

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.