Like wasserpest said, there is a lot of personal taste involved. A lot of aquascapers in South East Asia really like walls of moss or liverworts-- though it is a trade off like I mentioned above. Amano has never used a moss wall, and I'm pretty sure it's for the reason I mentioned. Once again though, such a wall is an eye-catcher.
About the issue of groups v. spread out, I'm suggesting compromise. There are some aquaria, especially "garden style" tanks. Organized groups are put together throughout. If you like European flower gardens, that style may be attractive. Nature aquarists, including myself though, will tell you that this type of scape feels life-less, and lacking in harmony. It looks artificial-- because it is.
In any given enviroment in nature, be it a meadow or a jungle, it is rare to find spots in the same environment where a plant can grow in one spot, but cannot grow in a spot within two feet of it (unless lighitng interferes, and there is no interference in your tank). In otherwords if the environment is suited to the moss where it is, than it is also suited where the vals are, and visa-versa. Therefore, it makes sense for plants to be growing in more than one place in the tank.
On one side, the danger is putting all the plants all over, which will make the display look monotonous, and un-exciting.
On the other side, making the plants appear in only one place, and giving each plant a specific section, will look artificial.
The compromise is to group plants, but to group them in multiple groups that can range in size. 3 groups is popular, especially with support plants such as bolbitis and anubias. With foreground and mid-ground plants, mixing can also be effective-- or planting slightly taller plants to highlight shorter ones in the foreground.
Background plants, especially red stem plants are a bit trickier, because they often draw a lot of attention, and may weaken each other in multiple groups. Tall grassy plants like vals, sagitteria natans, giant hair grass and taller crypts can be grown in single groups that are very impressive, or be used as high-lights spread amongst various stem plant groups.
Ultimately, the "rules" of all styles are guidlines only-- they're made to be broken, or compromised between. You go with a few, and do what you can to make it look good. Man do I talk too much when I get going. Shutting up now-- later.
Edit: PS-- I didn't really comment on your middle background, because I like it! It's pretty strong!