Yes and no.
The privacy extensions will create new addresses, but they will always belong to the same /64. To my knowledge, TWC will allocate a /64, but there's no guarantee that power cycling your modem will generate a new /64[0]. I believe other ISPs work the same way - they may give you a new /64, but they're not required to and don't guarantee it in the SLA. And most people won't power cycle their modems often anyway, which means they could have the same /64 for months on end.
If we're talking about online tracking, it's very easy for trackers to just throw their hands up and treat all addresses within a /64 as if they represent a single user + device. This isn't completely accurate, but it's no less accurate than IP address tracking with IPv4.
Furthermore, I am unaware of any reliable commercial VPN providers that currently provide IPv6 connections (at least over OpenVPN[1]), so if you have dual-stack connectivity, your IPv6 connection can compromise your privacy even for your IPv4 connection[2].
[0] Technically this is true for ipv4 as well, but due to the relative scarcity of addresses you're less likely to get a pseudo-static ipv4 address.
[1] OpenVPN now supports IPv6 clients, though I don't know of any actual deployments of this. PPTP is IPv4-only.
[2] I think this blog post is sadly still accurate: https://blog.dave.io/2011/06/vpn-ipv6-privacy/
