There are "active gliding sites" then there are "gliding sites on the chart". Some of them you don't see a glider on the field even when you fly over. Some you see lots in the air.
I wouldn't NOT fly over one, I'd just be extremely cautious and make sure I am above any cables, and it also depends on the weather. If it is not good gliding weather then you might not see a single glider. If it is perfect weather, you might see lots.
Just keep a good lookout.
Trouble with your average spamcan pilot is he or she is typically spending more time looking inside the cockpit than out, navigating with the latest gadgets,
Got an evidence for that? I like to look out AND use gadgets.