Three hours a week is hardly what I would consider to be a lot of meetings. Some of my managers spend 4-7 hours a day in meetings. Remember as you get promoted, the time you are expected to be in meeting will increase substantially. So attending and contributing to meetings is one of those things that can get you recognized as someone to promote. I suspect your boss is trying to get you noticed by having you attend these meetings. It could be a professional compliment not an undue obligation.
Since your boss feels the meetings are important, they are important. So try to make them useful to you.
First, make sure you brief your boss on anything that came up in a meeting he didn't attend that might be important to him. He might have you there because he can't attend or has another meeting. By considering his needs rather than just yours, you may find that there is information being passed that he needs to know about. Sometimes that information may be about your observations of the political alliances of other people.
Consider working with others to get agendas for the meetings. Likely some of them would also prefer to have agendas, so they can spend less time and know in advance what will be discussed. It also helps people be prepared for what comes up. With agendas, you can talk to the boss about what he expects to get out of this specific meeting. That might help you get out of some of them. It might also help you understand why he wants you to attend the meetings and what he thinks you should be paying the most attention to.
Contribute to the meetings. Meetings are a place for you to shine in front of people you don't work with daily. Just becasue the subject is not immediately useful to your department, it may be helpful to the company as a whole and having an input into solving a company problem is a good thing. Sometimes your outside perspective will help them see things differently.
Don't just wait for the leaders to pull the meeting back into focus, you can say things like, "We've gone off into the weeds now, we really need to concentrate on XYZ. Maybe A and B could discuss this outside the meeting since the rest of us are not involved." You don't have to be the organizer of the meeting to get it back on track and get it ended sooner rather than later. If you aren't part of the solution, you are part of the problem of the unfocused meetings.
Next use the meetings as a way to make connections to other departments. You say your group doesn't need those connections, but I have found that is rarely true. As a developer my connections to other departments are critical to the success of my projects, as an analyst, they were critical to being able to get things done fast (you know who to go to for what info), as an editor, they were critical to getting my changes respected and implemented. I can think of no department I have ever seen in any large or small organization that exists wholy outside of the need to deal with other departments occasionally. Clearly your boss thinks these connections are important, too, or he wouldn't make you attend.
One way that the connections are important to yuou personally is in getting your performance recognized and in getting promoted. Typically high performance ratings are limited in number for budgetary reasons, so all the high performance ratings are discussed ina senior manager's meeting. Those people that these managers don't know or have never heard of have a 0% chance of getting the highest ratings and pay raises. Promotions often involve people beyond your immediate boss. Meetings are critical to these people getting to know you. Of course if you blow off the meeting by acting like a spoiled, bored child, you don't make points with these people either. So be professional and contribute. It could be rewarding financially.