Size 2: What's viable for a town of Thornbury's size?

How many supermarkets, high street names and small independent traders could be financially viable in Thornbury? So many businesses are falling into administration that one wonders how long it will be before the majority of our town centre shops are either empty or occupied by building societies, banks, estate agents and charity shops.
How many commercial and light industrial enterprises could we service with premises and staff? Once again not a thriving sector with at least one large office block lying empty.
How much potential do we have as a dormitory town?
Answers to questions such as these would help to define the flow of income into the town and that in turn would enable a judgement on the type and scale of facilities that we could afford.
A simple example of the balance that must be struck is provided by ACT's promotion of Thornbury's very own 500 seat theatre. We already have the Armstrong Hall which is capable of seating over 300 and is used by Thornbury Arts Festival for a week each year to stage professional events which are by and large well supported. We also have several other smaller venues which are regularly used by amateur groups and for 'one off' events. But is Thornbury disadvantaged compared with other rural towns of comparable size?
A trawl through rural theatres in Gloucestershire, Somerset and Wiltshire and a few further afield shows that most towns of Thornbury's size don't even have a venue comparable to the Armstrong Hall. Those that do have a theatre are presented in the attached plot:

Let's focus on the those towns with a very similar population to Thornbury, i.e. around 15,000. The most significan outliers are the Pavilion at Whitby and Theatr Brycheinog at Brecon (both selected by the study for ACT) and Monmouth's Savoy and Blake theatres (amongst the others I've trawled). It doesn't take much thought to work out that these benefit from circumstances that are unavailable to Thornbury. So it looks as if Thornbury is already blessed with quite a large auditorium for a town of its size.
Of course size isn't everything. Undeniably the facilities at the Armstrong Hall need updating and fund raising is well under way to improve backstage. Whether we need or can afford the running costs for a state of the art 500 seat theatre is a matter for debate - one based on a sound business case, a realistic assessment of financial viability and hopefully no need for a subsidy by Thornbury folk.