That's interesting, because the very act of adding and IPv6 address to the LAN interface should cause that /64 route to appear in the routing table. For instance, on my autoconfigured XP box:
Publish Type Met Prefix Idx Gateway/Interface Name
------- -------- ---- ------------------------ --- ---------------------
no Autoconf 10 2001::/32 8 Teredo Tunneling Pseudo-Interface
no Autoconf 8 2001:db8:1234::/64 4 Wireless Network Connection
no Autoconf 256 ::/0 4 fe80::250:daff:fe53:6564
If you see the 2nd entry, that exists because my wifi interface autoconfigured an IPv6 address in that /64 subnet of my routed /48. What I was thinking is that to set the public flag on the existing route, you'd use the "netsh int ipv6 set route" command instead of "add route", since the route was already there. I figured if you didn't it'd give you a duplicate entry error. But I hadn't tested any of that. :shrug:
I'm not sure why you're getting that behavior with whatismyipv6. But the showip extension doesn't actually show the address you are using to actually connect to the site, but basically shows the result of a DNS call and its guess of which address your system would use. At least that's what others have said and I think I read the same on the homepage of that extension. I have some evidence that this is the case from a few times where my IPv6 connectivity went down due to something I did, and it still showed the IPv6 in FF even though I was really connecting via IPv4.
As far as not being able to get in from the outside, since you're on a windows box, it's probably windows firewall. You can probably configure it to let various things in, like SSH. If you can get to the IPv6 internet from machines behind your tunnel router, you don't have a routing issue.