Best Method of Handling Repeated Content Within Existing Fields?
Forgive me but after re-reading everyone's input, I lean towards Moto_Nomad relationships suggestion, mostly because it will make life as easy as possible for the content-administrator.

In your latest comment you write:


  ...but the issue is not about relating entries, but smaller bits of information, for which there is not a prescribed location.


Q: Could you give us an example of a 'smaller bit of information', please?


  That is, there are bits of information which could be used nearly anywhere within the CMS (things like the event booking link, booking deadline, event start date etc etc)


I'd suggest that the 'smaller bits of information' as well as the info you mention above, which are relevant to a Festival/Event should be stored within those (Event) Entries. 

Especially if these 'bits of info' are updated over time i.e. from from one event to the next.

(I'll avoid going into an explanation of the Entries field type) 

;)


  The ideal solution would be that these bits of information are housed in one place in the CMS (probably will be a global), and can cleanly be pulled through to other areas of the CMS with a super user-friendly bit of syntax.


Check out this thread: Is it possible to use Twig in a Rich Text Field?

I realise the above is about the Front-End but thought it might be useful.

Let us know how you get on, Mike :)