Turtle: I can't tell from your photo if that PVC feed line is sitting in the bottom of the channell/whatever or if the photo is upside down [maybe just my brain is]. If it is, then the long mat the roots will form will definitely cover it, pretty damn fast! If you already built what's in the photo then you can fix it by using Rigid Risers. They look like 10" pieces of 1/4" black dripline, but the walls are real thick so it's rigid -- stands up like a piece of PVC pipe would.
Cut a section of it a few inches long (however high you want your sprayers to be), then use 10/32 threaded connectors. Screw one end of the threaded connector into the threaded hole that your sprayhead's screwed into now [in the photo]. Then screw a section of Rigid Riser onto the other end of the threaded connector (the Risers aren't threaded, you just cut your own threads into them by screwing it onto the threaded connector).
Finally, screw your spray/mist-head onto the top of the Riser, and now the sprayer sits too high up for the rootmat to grow over. BTW [very important point], the sprayers have to sit BETWEEN the plant sites, not directly under them, or obviously the roots will descend on top of them.
Have fun playing. Personally I won't deal with anything that clogs in the future.
Here are links to those items, hope they work, and here's a photo of what I'm talking about that I got off the Internet.

http://www.dripworksusa.com/store/stakes.html

http://www.dripworksusa.com/store/mfit14.html