In 500 or so hours, I've seen at least 4 or 5 Mylar Baloons at altitude
(although I don't think at 10,000'). So you are about right.

Must be a Left Coast thing. I can't say that I've seen more than one
or two party balloons in the 1600 or so hours Mary and I have been
airborne...

I've seen quite a few R/C planes, but only when we flew over their
local airfield.

And we saw a humongous rocket, once. (It was NOTAM'd, and ATC warned
us about them...)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"