It appears that the most convenient way to extract contacts and other data from old Samsung Kies backups (.sbu) is to use some of the dedicated SBU handling utilities, for example the SBU Extractor. This utility should be capable to easily export your contacts from .sbu files and save them as vCard .vcf file.
Convert Samsung Kies backup to vCard contacts.
We found one software available in the database for this conversion.
Articles and other information relating to sbu into vcf conversion:
How to extract contacts and other data from Samsung Kies SBU backups - Getting mobile contacts out of SBU files
Microsoft Windows software - convert sbu to vcf on Windows
A program for extracting SBU archives
Convert from sbu file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.