Can't prevent Excel for Mac 2011 from opening all files at startup.
The option in Preferences, General to open all files at startup is deselected, however Excel still tries to open all files whenever Excel opens. Even when using Finder to select just one file, Excel tries to open all files.
If it's truly related to Resume, then holding down the Opt key while quitting SHOULD do the same as closing all files before quitting.
And if the files aren't saved in one of the two locations that XL uses for startup files (e.g., HD/Applications/Microsoft Office 2011/Office/Startup/Excel/ and whatever folder is entered in Preferences/General/Open all files in...), then the only thing
I can think of is a Prefs issue.
Try, with all Office apps closed, blowing away your prefs, as above, but adding this one: