As for the advantages, now you have an universal platform independant interface to insert data into database. Everyone else could have their own UI on any platform which invokes your APIs.
在网上填写数据 is something webservice can't do alone. You have to have some frontend application to display the interface to final user (say, asp.net or windows forms).
Aside from that, everything else is just fine for webservice. The frontend could orgnize the user inputs as xml data and invoke webservice afterwards. Or, it could simply pass the .xls file to webservice as binary and let webservice parse it (uses DIME or WS-Attachment).