To concur with a lot of folks here, I think cymbal lines are a great addition to any corps.
That being said, though, cymbal lines are one of those things you shouldn't go halfway with. If you didn't have anyone who could teach sabre to your colorguard, would you still utilize them? I think this is why, nowadays, a lot of folks see cymbal lines as "lame"; usually their only exposure to them is of the not-so-good ones they see from bad bands/corps, or ones on tv/the movies. I bet if you showed those same people a video of the really happening cymbal lines of the past 10 years, they just might change their attitude. (SCV, Spirit, Bluecoats [when they had one], Reading Bucs, Music City Mystique, Aftermath come to mind...and more....)
As someone else pointed out, those cymbal line members of the corps become the example and standard by which both the drumline and hornline are held to. It's not a pride thing...it's just that doing cymbals "the right way" shares a LOT of discipline and technique from both sections of the corps. Heck, even a little quasi-guard/characterization work thrown in, too. It's just the nature of the beast. It really is a thing all it's own.
True, field cymbals won't sustain as long as your pit cymbals; but that's because they're played differently. Beat a piece of metal in your hand, and then hang it from a string and hit it again. Of course it's going to make two different sounds. But having a cymbal line also means giving more students an opportuntiy to get on the field and make a great visual contribution, too, and not just a musical one playing swells when the horns and drums are blasting and you won't hear the marimba.
I could go for days on this...
And you wish they were going away? I dare you to try it yourself.