There was wider political participation in the era of state conventions than after the reformers brought in the primaries. In local communities the politically committed asked their neighbors to get involved and help them become delegates. Either way voter participation was up and the voter's knowledge of politics was more personal. Now we have the primaries and the presidential contenders broadcasting their media ads at an inert electorate. Few neighbors come to our homes asking for support for anything.
People stay home and watch the candidates perform in the fantasyland of television.
Allow me a prediction. The primary system is going to be replaced. Tom Wolfe has written that the 1990's would be the era of relearning. He may have been off by a decade. The next decade will be the era of relearning, and relearning the value of state political conventions and smoke-filled rooms will be part of the process.