My tanks have seriously almost all ended up mish-mashed and overgrown. It can hurt water quality if there is a lot of die off at the bottom. One thing to remember is that photos of people's tanks, like Amano and such, are taken at their peak, just before trimming (usually...not 100%, but usually).
I made the mistake of thinking that if I had a ton of plants, it would look lush. Sometimes just 2 species or even 1 species in a small tank can be very beautiful. Another point is that you don't want the actual plants to take up the whole picture. Not that splash paintings aren't interesting in their own rights, but the canvas of your tank can quickly end up like a bunch of paint spilling on the picture rather than a well thought out Monet.
The best tanks, IMO, are the ones that find the balance between open space, plants, and other aquascaping.