Speed and bandwidth didn't matter to me, so I held onto my DOCSIS 2.0 until it finally perished. When I exchanged it at a Cox Service Center, the representative wanted to charge me. I don't remember if Cox charged me for the original modem during my initial setup (I'm sure they did), but I wasn't paying an inflated price to replace a broken Cox modem.
I was anticipating a reason to experience another provider, so I asked the rep to cancel my account. The rep rewarded my loyalty...I'm still with Cox...and speed/bandwidth still don't matter to me.
The upgrade worked in my favor but if you have to finally replace your modem, you should buy your own. I'm sure a moderator can provide a link to their list of compatible modems.