I can't even remotely see what would be unethical about this!!!
They are your miles, you are outlaying them in order to accomplish this, and in addition, you will pay a $100 fee to cancel and redeposit. So what's the problem here?
I can't see why they wouldn't let you book both on the same days either. That doesn't make sense. I thought you could make duplicate res's only when it was on the same exact flights.
Im sorry, this whole thing makes me laugh!! That you even had to ask if this was unethical!
And to put everything on the table, I don't even have enough miles to do something like this, so I would be one who would be a/effected by what you do, and I could care less.
When you stop to think about it, such a small percentage of the population would ever even think of this.
-A