Thanks for your suggestions. I found the TeX mdimporter ( http://www.spookyhill.net/~gall/latex/#mdimporter) -- which is now part of the TeXShop bundle -- installed it and ran
mdimport /PathToFiles/ToImport
in Terminal (replaced /PathToFiles/ToImport with the actual path, of course) to import my LaTeX files. Spotlight now sees them!
Thanks for your help!
Wolter