"we have fairly frequent meetings with either ill-defined agendas, or agendas that are a long list of subjects with no central theme" - I am afraid you are missing the whole point of meetings here.
Meetings usually do have one quite clear and straightforward, yet hidden agenda. Meetings are a ritual for establishing and affirming the manager's presence and power. This is the corporate equivalent of an officer lining his troops.
Just by having to show up on time, possibly wait, listen, nod in agreement, report what you are doing, explain yourself over this or that, etc, you:
(1) prove your allegiance to the manager;
(2) keep up your psyche in a habit of obeying them;
(3) expose yourself, thus allowing them to notice any disturbing trends in the team mood (e.g. not being enthusiastic, not showing interest, not abiding by the unwritten culture codes, etc).
Of course, there are subtle and time-efficient methods to achieve the above, but do not forget that most entrepreneurs and mid-level managers are there to exercise power on the first place and make profits only on the second.
A meeting is nothing but a w*nkjob for a manager's narcissism - and corporate environment is among the most favourable and fertile environments for growing narcissism.
Figuring out the whole game is a hard pill to swallow for people who are dedicated to their work. But, for good or bad, that is how employment works. If you want to concentrate on your professionalism, talent and self-improvement, you can pursue freelancing or entrepreneurship, or some occasionally milder version of the employment model.
But, in all cases, do not engage into exposing the futility of prolonged meetings or "inventing" better methods for team communication, or openly rebelling. You'd be on the losing side, because seemingly nonsense meetings are not something wrong (for the manager) which needs repair, they are something useful (for the manager), in disguise.