That stretch of highway in between Armenia and Salento is pretty good. It's definitely one of the best, if not the best highway in Colombia. Also, the coffee region is pretty safe, and I wouldn't worry too much about taking a taxi to Salento late night. Have you made accommodations in Salento yet? If you have, then I'm sure that your hotel can help you with an airport pickup. When my dad visited me a few years ago, we went to Salento, and coordinating a pickup from Pereira (Salento is close to both Pereira and Armenia) with our hotel was pretty easy. You're going to be flying into Armenia rather late, so I'd coordinate a pickup beforehand, just to be sure. You don't want to be stuck at the Armenia airport, or have to go through the process of haggling with a taxi driver at 12 in the morning. Also, I can almost guarantee any price quoted by an airport taxi driver at that hour, is going to be pretty high. If you're at the airport in Armenia and it's midnight, then you have zero options in terms of getting to Armenia besides taking a taxi at the airport. Those drivers know that, and won't be shy about using that to their advantage when quoting you a price.