Bare Bottom Tanks (Was: What freshwater tank-cleaning fish toleratesalt?)

Elane T wrote:

The two champion guppy breeders in town use our moderately hard
(170 ppm) tapwater with no salt. They keep cories in their tanks
to scavenge extra food. The other thing they do is to run barebottomed
tanks with old-fashioned box filters. The bare tanks are easy to
clean and the box filters aerate the water well without any risk of
sucking fry into an impeller.

I've been wondering what people's thoughts are on bare bottom tanks. I'm
trying a bare bottom tank now, and although it's easer to pick up the
fish waste, I'm a little concerned that the lack of substrate might be
stressing the fish somewhat, especially bottom dwellers like cories.

As an additional aside, how much cover for the fish (e.g.
rocks/wood/plants/epoxy castles ) should you have in the tank? Would
keeping fish in a completely barren tank stress them long term? Are
substrate/decoration purely an aesthetic issue for the humans involved?