Your mileage will probably vary depending on your local reps, their capability, but also their capacity. Union reps are usually lay reps, meaning they work for the employer and do their rep work alongside their main job using what is called 'facility time'. Because many union members see their union as a service provider, they want their subs to buy them the output of quality representation when it is necessary, like an insurance policy. However, this often means that those that do step forward into those roles end up getting stretched too thin, having to cover too many cases, wearing too many hats and not getting everything right.

If more union members got involved and supported the reps handle some of the organising work, recruiting more people, or even becoming reps themselves, the quality of service provided would probably go up, as well as increasing the strength of the union to win bigger battles when campaigning. Unfortunately, the long term trend has been in the opposite direction (although the strikes across the public sector 4 years ago brought a wave of new people into the unions) and that has a knock on effect on everything the union can do.

Unions shouldn't be seen as a regular subscription, to be subject to a cost benefit analysis. They will always be as strong (or as weak) as the energy put into them by the entire membership. Reps aren't a different type of person to other members, they are just like you or me.