Dumb but easy-to-answer question! :D
Ning To Jamroom
Hi Strumelia - No such thing as a dumb question
If you have also run the 'Manage Media' tool on your original import, and have the resulting folder with all referenced files copied from the original archive, then yes, its ok to delete the original archive. You can then import the newer archive over the original import.
What I would recommend though, assuming that your newer archive is complete and that your site is not live and has had no new signups or uploads (that you want to keep), is to run the import using the 'delete and re-import' mode on all items. The latest Import module has several fixes and changes from when I originally imported for you meaning that if you do it this way you can take advantage of the recent changes and efficiencies etc.
I can help with this re-import if you want?