Gliders are far from invisible seen hundreds of them its poor lookout that can lead to you not seeing them. If the glider is not operating in an atz then it has every right to be there and the see and avoid principal works just fine. Can't imagine you ever to operate through loads of gliders on final approach unless your lost or operating from an airfield that as recently gone commercial near an already long established gliding site. Having flown both power and glider still find sticking my head out the cockpit works best after all been talking to atc units who didn't tell me about fast moving military traffic, privately operated ex-mil hardware, light aeroplanes, and dare i say it gliders.
LOOKOUT