Great, Tomislav!
Thanks to the hint to use fresh SVN checkouts, I cleaned the whole path branches of \development\cs and \development\planeshift (according to the Compiling Guilde), built a fresh CS revision, and a fresh PS revision -- that turned the former "unresolved external symbols" into "could not load libcrystalspace_d.lib".
So I found out:
Earlier, CrystalSpace libs must have been built to
\development\cs\out\debug9\libs
where outdated libs from months ago caused the missing symbols; but now they get built to
\development\cs\out\debug9\libs\Win32
instead. So I wonder if I lost the sync between the CS output path and the PS import path somewhere. Maybe even the SLN files for PlaneShift are outdated? - Just a guess.