Speaking from a Statutory Road Association point of view I offer you the following:
You mention By-laws. If you have them that is great but it makes it cumbersome to put an amount of dues in there because any changes will require a By-law change. I think your mention that dues may change in the By-laws further confuses this issue. If you are going to mention dues in the By-laws I think it should just state by what method dues are assessed (road frontage, one amount for all, etc.), when they are due, late penalties and possibly what actions MAY be taken to pursue delinquent dues. As far as changing the dues amount, I think to keep it simple you would just put it in the warrant/agenda for your next meeting what you propose to do and that there will be a vote on it.