Nanos are great for a lot of reasons. I've been fairly obsessed with them in the past, doing FW planted nanos. I used to do things like brandon where I would try to architect it in such a way that when you photographed it, the appearance was of a very large tank. I even photoshopped carpet in under my 2.5g once, to scale of a 55g. Hehe! There's something neat about a little scene of glossostigma elatinoides and riccia fluitans in a (FW) nano that's visually appealing (in other words; fly). Same applies for nano reefs.
Another appeal is that they are more practical in my apartment/living situation. If I get a house, I'm totally going to make one of those super reefs in the wall, but for now ... I will hone my skill at working in a small space. When I'm *really* good at it, and then I have a house and can make my ocean in the wall, think of how well I will be able to utilize that space. Of course, one of my ideas is to keep A LOT of open sand in a huge aquarium and like, dump a whole crapload of LR in an area, like a stony mountain rising out of the underwater desert sands. Or maybe the rocky outcropping would have more of a "lonely tree" look to it. You know, how like many farm fields have the lonely tree ... all out in the back, surrounded by fields of wheat and soy or whatever ... the tree being a refuge for birds and other animals crossing the fields, it begins to look like an animal city. Wow, I digress ... but that's the vision I have of my ultimate reef.
Yet another thing I appreciate about a nano is that it's a more focused presentation of art. A very narrow project, you know? It's like writing a short story versus some big life's work. It's not an opus, it's a fun jaunt that you can learn from and then move on (change is at the heart of who we are).
Also, I guess I just like little miniature things. I used to do model airplanes and spend hours painting a 1cm tall plastic dude with the tip of a pin. and i had model trains and stuff like that.
Something about many small shapes giving a volumous appearance in a small space really appeals to me. The multitudes of little leaves / lobes/ whatever really has quite a nice effect in nature. Not only is REPETITION one of the 8 basics of all design, but nature has a really neat way of doing things. Ever notice how naturally occuring organics follow their pattern, but appear completely random at the same time? Think of a field of trees. They all look different, all are unique, all are individuals. But they are all the same. They all branch the same way, follow the same pattern, have trunks at the bottom and midway up start branching. Even further: plants of the same species have the same leaf distribution pattern. Leaves of 3, 4, 5 ... spirally, opposing, ladder arranged on the stem... it's a great thing that at once enforces the unity of a group while preserving the uniqueness of every individual element within.
Visual trickery and subliminal perception / visual manipulation are other interests of mine ... and it definitely applies to aquascaping. I could really go off about it forever, so I guess I should stop now. Here's my mantra for all things design, modified for reefy purposes:
It's not about what's actually in the tank, it's about what people see.