I don't know about actually paying more to put one in, but in my Cherokee,
it's slightly nice to have. I usually leave it set to IAS
(non-corrected), but once
in awhile when I'm bored at 9000', I'll check to see how much headwind I'm
fighting
between the TAS and GPS readouts....

After you've done that once or twice, you will know what your airspeed will
normally be at 9000 feet. From that point on, a glance at your GPS ground
speed will tell you precisely what kind of headwind you're up against.

I'm not saying it's not a useful doo-dad to have on board, but I sure
wouldn't pay extra for it.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"