A competent glider CFI is one who has the ability to instruct to PTS
private and commercial standards. If you want to learn advanced cross
country and racing skill then seek out a qualified mentor. There are
few instructors that have XC and racing skills that would rather spend
the weekend in the back of a trainer than go XC in their own ship.

I had 150 hours in gliders, a gold, and 2 diamonds when I applied for
my instructor certificate. I instructed at 2 US clubs, 1 UK club, and
also at a US commercial operator. I long ago gave it up for the
pleasures of racing my own ship. I satisfy my instructor needs by
giving instrument instruction, wings training, and flight reviews in
airplanes. I give tail wheel instruction if I need some excitement. I
can do all that before or after work on weekdays. That leaves the
weekends free for soaring.

Andy