I thought Vic was way overused too, but he was the only sentient hologram in Trek I liked.
He was a hologram. He knew he was a holgram. And that was ok. He accepted his lot in 'life.' Artificial intelligence doesn't always have to be a Pinocchio.
As for Sisko's singing, I think teenage me cringed when it first aired, but I think he's pretty awesome now.