Edit: Found a Meshlab on sourceforge but it doesn't say it supports .xsi format. I work natively in XSI so I'm not sure if this is the right tool or not.
I use the free mod tool Softimage 7.5. If you're using that you'll need an intermediary program to convert from *.lwo (which XSI can export) to Wavefront *.obj.
From their you can import the *.obj in Meshlab. Run the option to remove duplicate vertex and save it back to *.obj.
Make a backup or copy of your original XSI scene to ensure you don't lose anything.
In your original scene you'll need to delete the model but leave all the hard points and scene root material.
Import the "fixed" *.obj into the scene. Everything should still be lined up the same way following this process. You'll most likely need to recreate the tangent, but the uv-map should still be intact.
It's really not a complicated process once you get it up and running.
If that all fails for you, which I hope not because it's a great tool to start using, I can send you the files I converted.