That Arigata meiwaku thing. Isn't it just easier to sarcastically say thanks?
Not if you're explaining the event after the fact to somebody entirely else. Arigata meiwaku isn't what you say when it happens. It's the thing that happens. Also, sarcastically saying thanks would be missing the point. If you're able to be sarcastic about it without violating social convention, it's probably not arigata meiwaku.
For example, let's say you're the mailboy at a large company. You work Thursday through Monday because you have classes on Tuesdays and Wednesdays. The president of the company hears that his mailboys have to work weekends, and finds it tragic, so he announces that he's going to change your schedule to free up your weekend. You relay up the chain of command that no, you're perfectly happy with how things are, please don't change it. It would be inconvenient.
Then you show up at the company party the following week, the president asks you to come up while he's giving a speech, puts his arms around your shoulders and announces in front of the the entire company that he's heard of the terrible plight your department faces with such terrible hours, and in the kindness of his heart he has changed everyone's schedules to give you weekends off. Everyone cheers and he hands you the microphone.
Do you:
A) Sarcastically tell him thanks
B) Smile and thank him for what he's done
If you chose B, then what he did was arigata meiwaku.