You don't say what's in the Excel files (Users, Resources, something else?), but you can save the Excel files to CSV format. ImportX will import Resources from a CSV file. There are several extras that will import users from a CSV file. ImportUsersX is one of them. UserImport is another.
If you're importing Data to a custom table or tables, it would take a custom snippet, but if you set up the custom tables to use xPDO, the snippet is usually very simple.
TBH, I always write a custom PHP script to import any CSV stuff, so I haven't actually used any of the existing importing tools.
You might also find this helpful:
https://modx.com/learn/modx-college/migrating-from-wordpress/
