Here's what I'd do...
If cash flow is somewhat of an issue at this time, don't hesitate to use the miles, even though it doesn't appear to be a good usage of miles. The fact is that $180 can mean more or less to you at any given time in your life!
If the cash flow is not a significant issue at this point in time, then go ahead and buy the tickets and save the balance of miles for travel you might not make otherwise!