I am a fan of bare bottom tanks, It is much easier to remove poo, excess food, control nutrients, water perameters, and allows you to have high flow rates. I love bare bottom systems and mine has been very sucessful even with salt water corals. I have much less algae as well. Not to mention, the more rock and decor = more water displacement. In a smaller tank, water is premium.
Cons: some may not like the asthetics, but you could paint the outside bottom and/or sides
Also, you need good flow to get detritus sweeped off the bare bottom and over to the power filter pipe. Flow also helps the fish get needed exercise.
Yes, I know Bettas can be murdered by to much flow...My 80 Gallons an hour is not murdeous, but brisk. (0.66 gallons circulated a minute)
Having said that...I am looking into some black rock with some sort of asian decor. I am getting ideas now from looking thru this sites lovely set ups.