I had forgotten about these and downloaded them yesterday. They're exactly the type of documentation that Softimage is lacking for new (or less experienced) users like me. I wonder how many of the workflows described in these docs are obsolete? Perhaps a kind soul out there could provide an update? Pretty please?

As far as I can tell only the chapters 10 & 11 on Simulation are truly and utterly obsolete. The old particles do not exist anymore and I guess (but I'm not sure) the Rigid Body Simulation (chapter 12) in XSI 5 still was ODE-based, whereas later version switched to being PhysX based. But you still can work with ODE in Softimage AFAIK, so that shouldn't even be a problem...
There might be some other stuff that has changed/been improved upon, but I think that can be considered "minor". My personal experience is that while stuff changes, most of it has stayed intact, even if newer/better tools have become available additionally...
And you're better off with an old, good tutorial, than no good tutorial at all...

Do a search on youtube for 'softimage', filter by recent upload date, and check out all the xsi v7 tutorials, literally hundreds that the kind soul acemastermind has been uploading. All a lot more applicable than the v5 tuts.

Don't want to start a "tutorial war" here, but the one thing the XSI 5 written tutorials excelled at IMHO was their no-nonsense entry-level approach. They were meant to show a little bit of everything XSI 5 had to offer, something you hardly see in more recent tutorials.
And good WRITTEN tutorials have become exceedingly rare anyhow...