UPDATE: Useful review of music video trends in 2918, including the return of mega-budgets for a handful of elite artists:
Drake’s mates and Taylor Swift’s cosplay: exploring the 2018 music video
https://www.theguardian.com/music/2018/may/19/drakes-mates-and-taylor-swifts-cosplay-exploring-the-2018-music-video?CMP=Share_AndroidApp_Copy_to_clipboard
I was looking for some info on the 1D GCSE exam case study but spotted a number of great articles on here. So here's a few pointers based on the site.
You can find a bullet list I previously did summing up some key music industry points (with many links to posts) here.
AS CDS DISAPPEAR TOURS ARE JUST THE TICKET: 1D EXAMPLE

The likes of 1D aren't going to do that. They did sell VIP packages for gigs - something else I saw at a Depeche Mode gig, with multiple tiers including a basic that simply allowed you into the venue earlier to hear the soundcheck. I've blogged on Taylor Swift and Katy b Perry doing this, with fans paying a lot for a selfie opportunity. [meet-and-greets post]
The basic breakdown is clear though - most major artists (Indies too) will gain more from tours than album sales. Even combined with streaming (which is now bigger than physical sales and download sales combined) that remains the case. Getting onto TV ads, film/game OSTs are also potentially lucrative.