Updated XCode to 7.0.1 via the app store but it still shows itself at 6.4 in the app and missing the new features
I would do the following:


Open Xcode
Open Preferences
select Locations


If your command line tools and Xcode about box don't both say 7.0.1 (7A1001) then you might want to just delete Xcode using Launchpad and then re-open the App Store to download a clean copy of the app. If you want to purge old simulators and SDK from ~/Library/Developer, do that now as well after making a backup of things just in case. 



I had some issues with the beta versions of the app and deleting all traces of the app helped me with some document set download issues - perhaps your simulator issues are related to mixing versions between 6 and 7 too?