Xenomoose has continued to prove to be a particularly difficult person to find, for frustrating reasons. If you google "Xenomoose" right now, you will find tons of results for someone who has been on the internet since the mid 2000's and likes kaijus and Alien and a bunch of other things of monster movie kind, which would look to be our guy. But it would appear that someone else with very similar interests came up with the same username around the same time independently, as even when pressed, this "Xenomoose" insists that they are not the same one as ours. There's no easy way to tell which Xenomoose is which, but the unrelated Xenomoose seems to account for all recent search results. Basically, it's like a more intense version of the Vivus situation.
I did recently discover an archived old Sagan 4 forum thread where our Xenomoose mentioned being Gorgatron9000 on Spore. But so far, this has not led me anywhere useful. Maybe I'll find something on the Sporum archives.