I speak as a graduate of (and occasional lecturer at) another university, but Cranfield is THE specialist aeronautical university in the UK. It's based on an airfield (you can find it in the AIP, also called Cranfield), and has a specialist flying laboratory centre.
Unless they've changed recently, Cranfield only does postgraduate degrees, but you meet graduates with Cranfield specialist MSc degrees all over the British industry - and I can't think of many who haven't been very capable. So, yes it would be much more than just a shiny certificate (although presumably it is that as well).
I work in the light aircraft industry, and don't feel qualified to comment on big aeroplane careers. But, in the light and military industries my experience would suggest that your combination of flying experience plus something like the Cranfield MSc would open up a lot of very interesting work. Whether it pays well is another question, because very little pays as well as the airline industry, and most company Test Pilots and Flight Test Engineers will not get paid as well as most airline Captains and senior airline Engineers. But, that's not generally why they do it.
G