I don't think you'll find better food quality than Raku (open until 3:00 a.m.). What I like about Raku for a group is that adventurous and timid eaters can both enjoy it. You can spend a lot or a little. You can drink or not. I'd suggest reservations; it is often crowded late-night.
These are all in the Palazzo:
Carnevino's Taverna &Bar is open until 12am http://www.palazzolasvegas.com/carnevino.aspx
First Food & Bar open until 1am weekdays and to 4am weekends. http://www.palazzolasvegas.com/first.aspx
SushiSamba open until 1am Sun-Wed and 2am Th-Sat. http://www.palazzolasvegas.com/sushis...
On the Strip:
Stratta at the Wynn has a late night menu. 11:00PM-6:00AM
Off the Strip:
Musashi has a late night menu and drink specials. 11:00PM-4:00AM
Raku is open until 3:00AM
Bootleggers Bistro is open 24/7.
Old school Las Vegas Italian
BJ's Cocktail Lounge just east of the MGM is open 24/7
218 E. Tropicana Ave
Bartenders and waitresses wear lingerie.
Joyful House is open until 3:00AM
Old school Chinese
Does that help you?
3131 Las Vegas Blvd S, Las Vegas, NV 89109
Bradley Ogden and Julian Serrano are both open until 11, and Bartolotta is open until 11:30. I'm assuming this means they'll seat you until 11, not that they will cut you off from food at 11, but I might be wrong, although we had 9:45 reservations at Serrano last week and people were arriving as we were leaving, so you should be ok there.
3570 Las Vegas Blvd S, Las Vegas, NV 89109