Clarke/Boat Quay are the last places I'd recommend to hang out in Singapore. They are ok to see for five minutes each, and maybe to take a water taxi from one or the other.

But as far as hanging out... both are heavily peopled with pushy restaurant staff that will almost force you to sit down to eat their overpriced (like 5x city price) tourist meals, and drink their overpriced sodas. The only people who go there are tacky expats. It's for the crowd that travels halfway around the world, and then goes to Hard Rock Cafe and McDonalds. Singapore is such a clean, safe place that even the most "adventurous" places will not pose a health or safety hazard to you -- you don't need tourist hangouts like the Quays.

My recommendation for late-night hanging out in Singapore is to ask the cab to take you to anywhere on Orchard Road (near Takashimaya is a good starting point), or to the People's Park shopping center. Lots of nice, safe walking around, and excellent food. Food and cabs are cheap. One late-night caveat: because of the after-midnight cab surcharge, it's difficult to find a cab between about 11:00PM and midnight (there is an unspoken cabbie cartel agreement not to pick up passengers right before the midnight surcharge kicks in).

I always enjoy late-night wanderings in Singapore after my plane arrives; I'm sure you will too. Happy travels.