I hope this isn't a dupe; I've searched for other similar
comments but didn't find any.

I also hope I'm not treading into religious territory. :)
I sincerely don't intend to, but I'm afraid I might be. :)

People are pretty used to using the left mouse button in
web browsers & non-spatial file-managers to go to a site
w/o opening a new window, and using the middle mouse button
to open a second window.

So, personally, I think mousing would be more consistent if
nautilus reversed the meaning of the left & middle mouse
buttons.  (Left would pop a new window up and close the
current one, and middle would just open up a new window w/o
closing the current window.)

Or, equivalently, I'd be happy if the web-browsers reversed
their left & right mouse buttons to be consistent w/ nautilus.

I don't think there's an inherently "right" meaning for the
left & middle buttons;  it's just that I find unnecessary
inconsistency aesthetically displeasing. :)  I haven't done
any tests, and don't know what's actually easier on the user.

Also, and I know this is probably religious territory, too,
for consistency w/ the browsers I'd also suggest moving to
single-click as the default in Nautilus.  I've found it easier
to teach new people to use GNOME w/ single-click everywhere,
but that's certainly not good user-interface research. :)

(Btw., thanks for switching to spatial.  I was seriously
disappointed that Eazel went for an Explorer-like model in
the beginning...  this is a great improvement.)