The 18-300 is pretty darn good for what it is. I have one and have not gotten rid of it because of it's versatility. I prefer my Tokina 16-50mm for most things, but as a travel lens lens(assuming you're not there solely for photography) it's hard to beat.
My problem is I've had a hard time deciding what would be most useful. I can't really go on a buying spree with lenses, and I'd like to get something that is good quality and also useful through a reasonable zoom range so that one lens would mostly do all I want as a walk around camera. These newer zoom lenses are interesting because they are all relatively the same size and weight, whether it's the 16-80, the 18-300 or the 18-140. A long time ago, the longer zoom range would be much longer and heavier than now.
So it comes down to what is most versatile and also is capable of very good quality. I had the 18-70 on my D70s for 14 years and was generally satisfied with that range, but in those 14 years I had mostly abandoned photography as a hobby so I hadn't looked for anything else and wasn't missing having other lenses. I wouldn't bother with ILCs at this point EXCEPT I really want to play with wider angles than 16 or 18, so I need to be able to get a second lens for wider angle. Ideally I'd like the 18-300 for the range, but if the 16-80 is as good as most people seem to say it is, I'm interested in it for the extra width it gets (from 16mm), although I don't know how much wider than 18 that would actually be. Perhaps I'd be happy with 16mm and wouldn't even feel the need to find a 10-18 or 10-24 type wide angle second lens. And it would be nice to have the 300 at the other end. I like the idea of the 2.8 on the 16-80 (faster than most zooms out there), although it sounds like that shifts quickly out of 2.8 anyway so I don't know how useful that would be overall.
Decisions, decisions, but I appreciate all the viewpoints you folks are posting.