It coaxed some neighbors into the process who might never have gotten into the process. And it probably lessened the influence of money in presidential campaigns. Now that last thought should fetch the interest of today's advocates of ill-conceived reforms, to wit the advocates of campaign finance reform. The primaries are immensely expensive. State conventions cost individual candidates little by comparison.
Party organizations do the bulk of the work, much of it with volunteers.
Expensive television ads recede in importance and the personal involvement of a wider range of citizens grows. That is what reformers wanted in the 1960s. They could have it today with a return to state conventions. Reformers, my advice is to take a step backward into the past. That will move you forward into the future.