According to jisho.org, both 行き先 and 旅行先 both have the meaning "destination". My intuitive guess is that 旅行先 is the destination of a trip, like "this cruise's destination is Bali" and 行き先 would be a more generic endpoint, like the destination of a train or a taxi ride. Can people clarify the difference in usage between these two words?
A 行き先 is the place your transportation takes you. When you get off, your journey is done, and that's the end of it.
A 旅行先 is the place you go on a trip away from home - you get there, and then you stay there for a while, and then you come back. This is typically for vacations, and a good translation might be 'vacation destination'. The core idea is that you're not 'done' with your trip once you get there - the point is being there once you arrive, not going in the first place.
A short example might clear it up. If you're going on vacation to the Philippines, you have a 旅行先 (the Philippines), but the plane you take has a 行き先 (probably Manila, though you might also say 'the Philippines').
You are right. 行き先 is generally a destination, and 旅行先 is a destination of a trip. That's all.
But if you want to say "the destination of the trip", 旅行の行き先 is far better than 旅行の旅行先, as you should avoid repeating the same word.
Therefore the word 旅行先 is not so common. One of the good places to use this word is (which I found by googling it), where you want to bring both 旅行 and its 行き先 to the context at the same time, as in
人気の海外旅行先ランキング that is a title of a webpage.