"These days if a client wastes my time, I just console myself in the fact that they're paying me by the hour."
Exactly that. I learned that giving 150% and being highly efficient is much like kicking the ball into your own goal. If the client feels like arranging tons of meetings for absolutely no outcome... fine. Most of the time you don't need to listen, as very little is going to come out of meetings with too many participants. Just nod, look interest, throw in some related but mostly random thoughts to give them more food for thought...
Extra brownie points if somebody comes up with a power point presentation. Make sure to feign interest by checking early on that it's available on the company's intranet or is forwarded to you by email afterwards. At that point you could actually take a nap and it wouldn't matter. (If you miss anything important, you can still catch up later.)
Otherwise, enjoy free coffee and cookies, and look forward to being a few hundred quid richer at the end of the day (with a new highscore in your favourite tablet-based game).
I seems to work a lot better not to ever suggest big changes (they're just not ready for it, and likely never will be). Instead, make small improvements here and there and wrap them into big and impressive lingo which nobody grasps anyway. So it must be great!
Also: Never fix anything immediately, if it can be delayed. Ask for deadlines, importance in relation to all the other things you've been postponing, make it sound more work than it actually is! It makes you look very busy and avoids that anybody of those paying you might think they pay money for somebody who hasn't got enough to do!
Companies don't like to end a contract if you're still in the middle of something they think is important (because you made it sound like that). So better make sure that they think you haven't finished all tasks, ever.
Then you get away with 50% of your energy left to spend on your hobbies after hours, and you keep the contract longer (because, well, you're not actually working that much any more).
And when shit hits the fan and you actually have to deliver something very quickly because it's critical, do it, but point out the other deadlines and ask for them to be pushed forward.
Kept myself with a corporate client on a contract for over 4 years that way... and now they are still paying a retainer, because they think they might need me for urgent stuff. (They don't actually, but that doesn't matter.)