You're right--the tops of your teaching skis will be demolished! But it won't affect the way they work....
Actually, the choice of skis for teaching has never been easier. When students all started on 150's, and instructors all skied on 200-210's, it was difficult sometimes to demonstrate in a way that was meaningful for the students. Some instructors got special short skis just for teaching. But that didn't work very well if you showed up to lineup and got a high-level lesson. Or if work was slim and you wanted to go take a few runs--you had to go back inside and switch skis. I have never enjoyed teaching on skis that I don't enjoy skiing on!
But now, there are so many great, high-end, versatile skis that are 170cm or shorter that it is easier to teach on your performance skis. So teach on your "good" skis. You'll cringe the first few times they get skied over, but you'll get over it!
Not to be contentious, but I don't support the strong suggestions here that you use twin-tips for teaching. Not that they wouldn't work great, but they aren't necessary. They solve a problem we don't have! It's a time-honored ski-teaching tradition to ski backwards in front of your students, and instructors have been doing it just fine without twin tips for many years. I have NEVER seen an instructor catch a tail and crash when skiing backwards on "regular" skis. So teach on twin-tips if you like twin-tips, but I wouldn't buy a pair just for teaching.
The big exception is if you teach in a program designed around the new very short (110-135cm) special beginners' skis. If so, you should be on the same skis they are on. And frankly, for reasons I can't explain, those tiny, low-performance skis are a blast to go out and rip around on after the lesson!