The BBJs are a good asset for VIP. They are small enough to land in places a wide-body could only dream. For example, Çanakkale Airport (near ANZAC cove), Paris Le-Bourget and Caen, France. All airports the BBJ has been in/out of. Other leaders needed to be driven in from larger airports further away. Even yesterday, Mackay and Bundaberg - wouldn't get anything bigger than a 737 into there. Richmond is a key VIP destination, major operational limitations on a wide-body there. Many South-Pacific and NZ airports are better suited to the 737.
There is a significant limitation - the two-stops required to reach Europe or Eastern USA (normally Singapore/Abu Dhabi and Honolulu/Oakland). Having said that, these trips are not as frequent as you might think, maybe a handful of long round the world trips a year. So a dedicated wide-body asset is overkill IMHO. Having said that, not being able to carry the media is a significant issue for modern Government. It has been overcome recently by having a RAAF KC30 shadow the BBJ for G20 and then having the second BBJ replace it after the Prince of Wales duties were complete. So yes one BBJ was just for the media.
The most significant limitation is lavatory waste space. On long sectors it's honestly one of the major reasons they tech stop (not fuel/range).
The BBJ can fly the RNP approaches into CBR now which helps during days of reduced visibility, something a wide-body would need certification for into there. CBR has performance limitations on a good-day, the wide-body would struggle to take a full payload and fuel for 12 hour sectors.
The aircraft is not a flying palace, Emirates First Class has better amenities. It doesn't even have a bed. Just lie-flat seating. It does have WIFI, a private bathroom and shower for the VIP and business class seating in the rear.
The CL64 can only carry 5-6 pax - rarely enough for the PMs entourage.
Keep in mind, I'd hazard a guess that nearly 30-40% of missions/taskings are training sorties to keep all the crew current (operating under EVY callsign).
The GG does get first use of the jet but it's mostly used for Govt and Defence work.