Engine Cover/Skid Guard -- necessary or not?

The partial Engine Cover in the front of my 2005 has a hard time staying attached to the front bumper cover. I know this is hardly a unique problem, as Toyota seemed to think that a few little clips and bolts through flimsy plastic tabs on the bumper cover would be sufficient to hold it on.

Of course, on a relatively low-slung car, driving in a hilly area, that's just not going to work. Several of the bolts/clips have been stripped off at this point, and those that haven't can't hold on, as the little "tabs" on the bumper cover have cracked and can no longer hold the bolts securely.

The cover itself is no worse for the wear, but I'm loathe to get an entirely new bumper cover just to fix this, when it'll likely break off all over again the second I (or another member of the family) hits a steep driveway or curb!

So my first question is this: can I just "do without" the cover? I know it imparts a (very tiny) aerodynamic advantage, but seems hardly worth 300 bucks when it might not even last. I'm more concerned about potential damage from dirt & debris flying up into the engine compartment. Driving in upstate NY means there's a ton of sand and gravel on the roads for half the year, and that's not very friendly to cars. Or is the "cover" that the prius has so small (and ahead of the wheels) that it doesn't really make much difference?

Second question: If I can't do without it, is there any way to "fix" it back into position in a way that won't require a new bumper cover? Right now I have it held up with some metal wire ties I looped through the grille, spoiler, and the holes in the cover... which *works*... but not very attractively, or securely.

Third: IF I can't do without it, and I can't fix it effectively without a new bumper cover, how can I fix it so that, barring a serious accident, I NEVER HAVE TO DO IT AGAIN? Are there any aftermarket parts that can attach to more secure anchors? I'm wondering if I could jerry-rig a little plate to the bumper cover and engine cover, a few inches IN from the edges... Though I'm not exactly great at hand-made solutions...