I have a small prairie planting. I planted my prairie, just as you describe, with tall species near the back and shorter ones in front. When a taller species reseeds near the front, I simply break or cut it off at ground level. the grasses fill in the void.

I also intentionally plant a lot of grasses near the front edge of the garden so that they occupy that area more strongly. I like the soft cohesive look of the grasses in front. If a shorter flowering species wants to play with the short grasses in front, that is usually fine with me. I especially love butterfly weed, sky blue aster and purple prairie clover near the front. I only have three species of grasses in my garden, little bluestem, side-oats grama and prairie dropseed which are all short in stature.

Other hints of prairie design:
Make sure that you always have something blooming throughout the year.
Limit the number of species so that the overall composition is not too cluttered--remember, you can always add more diversity later.
Choose plants that are not too aggressive. If there is an aggressive plant that you absolutely must have, be willing to keep it in check.
Avoid straight lines, but keep curbs gradual and large and make them make sense.
Design wide meandering paths of at least 6-8 feet.
Join a group like Wild Ones so that you can tour other local native gardens--especially, since your wife seems to be on the fence about this. Remember most importantly, "Happy wife, happy life!".

To further help you out, I've provided a link to an excellent article on prairie design.

Here is a link that might be useful: Native landscape design