Singapore's main strategic issues are balancing between Malaysia and Indonesia - and they keep on reasonable terms with both
China is important economically but you won't find many tears in S'pore over the movement of a lot of trading from HK - and S'pore Security is rumoured to be top rate with a lot of Israeli input
From a military point of view they run a very capable green water navy - plus a first class Air Force. I'd agree that its very unlikely they'd want SSN's - they're surrounded by really shallow water for a start so any operations would be a long way from home