It seems that some spreadsheet software still support old formats from Lotus 1-2-3, including the .wk4 files from version 4 of the program. Importing data from these files should be doable, but some of the original formatting (if any exists) will be most likely lost. However, this should not prevent you from conversion of .wk4 files to Excel formats.
You can also find utilities like the ABC Amber Lotus Converter, that were made specially for the purposes of export of conversion of old Lotus 1-2-3 spreadsheets and documents, including wk4 to xl conversion.