"As a general comment, it is usually best to buy a lens with a specific need in mind, not just to cover some perceived gap in the bag..."
Well, that is why we all end up with a drawer full of special lenses. I am one like that and worse. I have all different size camera bags, backpacks, slings, sleeves, rollers, etc. it is fun sometimes just to pack for a two week trip. That is why I begin to think minimalism. How can I pack just enough to cover most if not all situations, if only someone can develop a super duper zoom, like 18-200mm VR, but make it with f2.8. Have they?