From the military aviation side it's a little better, since mil
aircrew are trained to look outside for threats - and a glider can
kill you almost as effectively as a SAM! Plus, on the fighter side,
most have onboard air-to-air radar (which can detect gliders most of
the time, depending on speed over the ground) and transponder
interrogators (which unfortunately are not continuous like TCAS).
Transports/tankers/bomber are more like commercial jets, I would
imagine most have TCAS, and the newer ones (C-17, B-1/2) have HUDs.

What scares me more than the big jets (which are relatively easy to
see, and tend to fly predictable routes - and have TCAS) is the "fund
manager in a Cirrus". Beautiful glass cockpit, trophy wife in the
right seat, laptop open getting last minute work done on way to next
meeting...yeah, like he is looking out the window! And he is right
down in our altitudes. He likely has his transponder on, so PCAS will
help, but he may be VFR so your transponder may not.

Or the old guy in a beat up Tripacer, VFR, not talking or squawking to
anybody, and a windshield so covered in bugs and bird droppings he
can't see anything anyway.

IMO, PCAS is minimum equipment, then xponder as soon as can afford.
And use the attitude motorcycles riders have had to use for a long
time - plan on the other guy NOT seeing you!

Cheers!

Kirk