ArcGIS 10.2.1
.xls file (xlsx never works with any version of Arcgis, always get error: "Failed to connect to database. An underlying database error occurred. Class not registered")
My quick solution was to add a text field, copy all values from original field, adding a "_" character to all numeric values. Import table to GDB, edit in ArcView, copy all non numeric values from new field back to original one (where they were thrown out) and delete new field.
But the import tool should import text fields as text in the first place!!!!!!!