Many pieces are used over and over, and no one minds at all; they're classic pieces of musical literature that (most) everyone knows and respects. Bands play such pieces not because they're trying to be unoriginal, but so they can say that "Look how well we can play this." They're sort of a common denominator in that most everyone has heard that piece once or twice before, and so can compare. Other bands favor original compositions that show the band to be... well, original. Churchill as of late has done mostly original arrangements by Higgenbothem. The most popular trend as of recent years, however, seems to be a mix of the two. One notable band is Reagan; in their program description you can often find "classical" pieces, such as Symphony No. 1 in Bb or Profination (05), A Young Person's Guide to an Orchestra (04), or Aegean Festival (02). Their second movement in 03 was noted to have several excerpts from well-known pieces, such as Jupiter, Bolero, Malaguena, and Appalachian Spring. There were supposedly up to a dozen different clips in the second movement, but I figure it's closer to half that count. You'll also find, however, a lot of "Original compositions by..." They really like to have completely original stuff put into their shows, and that helps the creative side of it; it gives the directors the ability to change the music to fit the show, opposite of what normally happens. Or at least, that's how I see it. Nevertheless, the point is that many pieces are used over and over, but to answer your question, yes, there is a lot that is completely new and original in today's marching band.
Forgive any horrible mispellings, as I'm a poor speller.