Swiss at JFK T4 is thoroughly underwhelming...
I've only been in there for OZ flights, and each time, I've found it to get to around 70% full. Food options are ho-hum. My last flight out of JFK on OZ, I went and had a 'shroom burger at the T4 shake shack before heading to the swiss lounge to wait for my flight

And if the OP is flying Y as *G, then all you're getting at SIN is a slightly comfier seats and some free food and drinks. The krisflyer gold lounges don't even have toilets, let alone showers...

If you're flying J, then head to the silverkris lounge at t3. it's a bit nicer than the one at t2.