Good question. Did see an article recently about the merit of a one club Bristol United FC for glory approach, but seems there's no appetite for it. It also mentioned the side effect of the competing traditional rugby support base within the west country. With the Bears and Chiefs in ascendancy, this has made an impact on football gates in recent years, I know that. Not been aware of a similar rugby following in Swindon, other than seeing the occasional Bath (or Gloucester) cap/shirt ?
Geography obviously plays a part too certainly in the deepest parts of the west country. Rather than move and uproot his family Tisdale used to commute daily from Biddestone, and did so for 12 years, and a car load of Bristol-based players would do the same. Always been a problem down there, recruiting players/managers, being out on a limb. Again, I wouldn't think that would be such a problem for Town, is it ?
Since the mid 80's Swindon never seemed to struggle attracting quality managers and read an interesting article a while back that in general Bristol City could never get big names to join them because it's too far away from London, Surrey and the Home Counties as it can be upto a two hour drive each way with Swindon only being an hour. I don't think the emergence of Bristol Bears rugby has affected the football crowds as the the last couple of seasons they've have overnight 13,000 season ticket holders and average crowds have been around the 20k and Plymouths attendances have also been pretty good considering Exeter chiefs is just down the road but as you say they are out on a limb so will always struggle to attract decent players and managers even though it's a lovely part of the country. As for Bath & Gloucester rugby taking support away from Swindon I doubt it very much as I know a few who follow either team but aren't really interested in football and in general it seems to be a completely different fanbase.