Hello,
Old .vst files need to opened in Cubase SX3 and saved as a .cpr file.
In SX3:
File>Import>Cubase Song
File>Save As for .cpr
If the projects are MIDI, then the next step is
File>Export SMF (standard midi file)
Better yet, if you still have access to Cubase VST, I'm not sure at the moment, but you may be able to export to SMF from the File menu.
The SMF can then be opened in Logic or any other DAW.
If you don't have SX3, I can convert the files on the 22nd or 23rd of this month when I'll have access to my set up.