There is no right or wrong answer to this, but I'm interested in comments and thoughts and photos of other layouts.
I visited a very gracious forum member yesterday who had invited me to look over his layout. It was perhaps half again the size of mine, but had, quite literally, six to eight times as many buildings, streets, accessories, vehicles, etc., on it, as my layout does. Every square inch of benchtop was covered with track, trains, accessories, buildings, vignettes, etc. There was something interesting and fun to see everywhere you looked. It was truly fantastic - more fun in a small place than I've seen in ages. I spent two hours and didn't see nearly all of the fun detail crammed in all that space.
I've gone for a completely different approach on my layout, as you see in the photos below. I do have a town and buildings (not shown) - thrity-one to be exact - but over half of my layout is "open country" in which I have only a single building. A layout like this has a type of beauty and representation that I want - in this case of southern Colorado around Raton Pass, where I spent a lot of time when I was a kid -but it means I miss out on a lot of fun: six to eight times as many buildings means, in many ways, six to eight times as much fun building them and six to eight times as much fun looking at the layout.
I don't really have a point here. In time maybe I will slowly fill up my countryside with buildings until its full. But on the other hand I love the open country majesty I get and the way open country allows the trains to stretch out and display themselves so well. I'm not ready to give my approach up anytime soon, but do realize it costs quite a bit in some ways: seems whatever size the layout is you can never have enough room for everything you want!
Santa Fe's 4199 pulling 11 flats full of tractors and containers meeting 3751 pulling 13 map-slogan cars up Raton Pass, while on my country road an eighteen wheeler also headed down from the pass meets a Greyhound bus headed up. The solitary building on this entire area of my layout - a country gas station/garage, is to the right.
There are many things that I love about my layout, but watching a long train wind its way through the pines by my mountain lake is one of the best.
Below, the opposite end of my layout (as the trains run - the layout is a U-shape so this scene is actually what you see when you have your back to the mountain lake) is also country, of a different type. In all, of 335 sq ft of benchtop, about 200, or 60%, is countrywith no buildings at all.