Nah, the TDU is much better than the tour of britain. The points system for races, which the UCI created does make a difference. They give the tour down under 100 points, same as the Paris Nice, Tour of Romandie, Pais Vasco etc. Since cycling relies a lot on tradition, and since it takes place earlier in the year, the TDU wont ever be as good as those races, but the points system certainatly raises its profile.
In Tennis Wimbledon used to be the most important grand slam, way better than the others. But for a while now the point system in tennis has given equal points to all the grand slams. Now they are seen as pretty much of the same importance. A gs is a gs, doesnt matter which one. If the gov body keeps saying that races are equal, they will keep moving closer to eachother in importance.
As for the tour of britain, that is not currently an important race. Britain, or at least england, is a country quite hostile to road cycling. For the race to improve, Britain would need some "darling of the public" to compete and raise the interest of the sport. It seems that it would need to be gc contender fighting for the yellow jersey. However perhaps Cav, if he wins the green jersey, the world championships and most importantly, the 2012 olympics. Those would be 3 seperate cav road cycling stories that would make the back/ front pages of the newspapers, and they would make him one of britains best known faces. Then, Britian would take road cycling more seriously, and take the steps needed to make it a bigger race.