I think that whilst it's good to boost your local scenes and be supportive and everything, that ‘Bristol exceptionalism’ can sometimes be self-defeating - I guess I'm agreeing with
BristolTechno above.
At certain times, under certain circumstances, Bristol has been able to nurture and sustain some awesome music - but equally there have been long stretches of stagnation. Nothing great ever lasts forever.
So for example having massive free musical events in the city like Bristol Community Festival/Ashton Court and the St. Paul's Festival/Carnival helped as a way of providing stages to be filled and audiences demanding of entertainment. A large number of music venues of varying size and scale - mostly independent, often quite grotty (and so often cheap for punters and easy to access for new artists seeking gigs) definitely helped - but times change, areas get gentrified; big entertainment companies set up their own concerns; new apartment blocks lead to noise complaints lead to venues closing down; land values increase meaning landlords can make more money selling up to developers that delapidated rehearsal studio or car park previously hired of a weekend to grey economy party entrepreneurs; increased police attention close down the best known squatted party locations - whether in town or outside it, industrial or rural; and so on.
When I moved the Bristol there was something of a perfect storm of conditions - Massive Attack and Tricky and Portishead had all had their albums come out; there was lots of ‘trip hop’ hype; the campaign against the CJA had been big and visible; there were lots of very sorted (and not-so-sorted) free party crews, often linked in to long-established free festival, traveller or punk milieux; relatively recent development work meant there were lots of newish-but-empty industrial units around easy distance of the city centre begging to be ‘borrowed’; equally, lower land values and poor reputation meant there were lots of cheap venues available across high population density, inner city areas; several long-running pirate radio stations; long-established antagonism/mistrust between communities and the police giving more ‘space’ to get away with rogueish, outlaw activity because your ordinary Bristolian would very often turn a blind eye to it in a way less common today; Ashton Court and St Paul's drawing peak crowds from all over, as well as other semi-regular free events like Respect in the West and Under One Sky (now almost all completely supplanted by paid-for, ticketed, commercial events taking place on fenced off public spaces); a more favourable population demographic which seemed to better sustainably balance long-established locals with interested incomers than the much higher numbers of students now coming here and almost exclusively living in student flats in socially cleansed city centre locations; etc etc.
Comes in waves though, doesn't it? I remember the early 2000s seemed a bit pants as the dynamic shifted from smaller and mid-sized independent, underground club venues with 6, 8, 10 hour nights three or four times a week - your Tropic/Loco/Maze, Lakota, Depot, Easton Community Centre, Trinity, Tube, Malcolm X and the rest - to bigger, shinier corporate concerns (Rock and the crappy harbourside ones in particular) and bars doing clubbish nights until 1 or 2. But then things picked up again with breakcore and dubstep and grime and a resurgent hip hop scene and DnB and whatnot, creating or consolidating their own infrastructures and ecosystems in the face of a hostile business environment (i.e. a more hands-on Plod, corporate shenaigans, council licensing, gentrification).
/Rambling