I've always been in the school of ride a lot and you will get stronger but just riding will not make you faster IMHO. I ride with many different level of riders and some of the faster guys ride way less than the riders in the slower groups. This is because the slower rider, although they may put on over 10000k a year do it all at the same 22km/h avg all the time with no thoughts of intervals hil repeats anything, just get out and ride. I started really seeing an improvement after two seasons then began doing intervals ETC and saw a greater improvment, then lost 40lbs and saw a huge improvement!