Raffles is a 5 minute walk from IC. I haven't stayed so nothing further to add but obviously it reproduces/preserves its old Singapore character. However, the IC does too, in the restored Peranakan Shophouse wings and the lobby (but maybe not quite on the same scale). The "vibrant city" feel at IC comes from being connected to the large Bugis Junction shopping mall. That may or may not be what you have in mind.

Others will know this better than I, but AFAIK these days the only places for hawker food in Singapore are the hawker centres. Lau Pa Sat has just reopened and although I didn't visit before its refurbishment I am going to bet that with each "upgrade" it loses a little of its authenticity. Patisserie and coffee chains now in evidence alongside the local specialities. Check out the Singapore forum for threads on Singapore food.

I suspect Haji Lane comes alive at night in a way that might be more what you are looking for - short stroll away.