Admittedly not knowing the precise home supports of clubs, only the overall attendances so far this season, will probably confuse the figures, but as far as I can see, the Dundee clubs draw in 9.5% of the city to see them. Aberdeen attracts around 6% of the city to Pittodrie. On the other hand, 0.5% of Glasgow are interested in Thistle.
Of course, Clyde, Clydebank, Hamilton, Motherwell, Airdrie, St Mirren and Greenock will all have similarly suffered losses to the Old Firm disproportionately to the rest of the country (though you'll still find a Celtic shop in every town in the country).
What will change this? Maybe a nicer stadium and some silverware? Neither did bugger all for St Mirren, really.