+1 for the sand!
Even if you don't have cories as your top option, the tank looks SPECTACULAR with sand, and economically speaking, you can get a 50lb bag for like $3. You can't get anything like that for the price with gravel. On top of that, I've seen countless threads on here where people switch after years of gravel, and they have been very good about gravel vaccing, yet there is a huge build-up of gunk that just can't be taken out of the tank! Sand will keep the detritus on the surface, and if you have enough circulation, most of it will end up in the filter, since it can't get stuck in the substrate.
Cories are a great choice, btw, and will pair nicely with almost any other peaceful fish you can think of!