I would imagine the earliest changes in bikes and tires made the MOST difference. Whereas today, we're on marginal gains.
GCN more than once has done a "budget superbike" for both road and TT to pretty fair success.
Even in Nascar with a pile of rules about making different cars "standardized" people over the years have gamed the rule book with ingenuity and cash. I remember stories of super long coiled up fuel lines to hold more fuel and their safety cage filled with BB's that were then released on the back of the track during a caution lap to free up weight.