The 180 is a lens with impeccable reputation and expensive, but the 150 is no slouch and I doubt you'd see any significant difference in most circumstances. I say save your money, and get the cheaper 250 (I got one in BGN condition from KEH very cheap) and use the 150/250 combo. The 250 is a great performer as well. As for telephotos in landscapes? Sure, for isolating scenes and giving a different compressed perspective such as "layers" of mountains fading in the distance. All up to what you're looking to do.