I'm an American leaving for a vacation in Australia on December 16, so I've been watching exchange rates pretty closely the last couple of months. Is a rate hike by the Fed likely to make my vacation more or less expensive?

Higher tend to lead to an appreciation in the currency. This is because high interest rates means saving in that country gives a better return. Therefore investors often move funds to countries with higher interest rates. Since the inflation rate is so low in the US, you should see the $$ value increase.

Seriously... speaking as someone who travels a great deal and deals with currency exchanges, and has done so for over 28 years..

If you are so strapped you can't afford a swing in the exchange rate... you really can't afford to be traveling.

Everything has to be planned in advance . Not just tickets but VISA's when needed etc...if a last minute currency swing is going to break the bank. You shouldn't be going. Because you couldn't afford any unexpected additional expenses which can always happen.