So, if you were to ask at the hotel, they would probably send the tourists to one of these, which are mostly good.
El Rey del Cabrito (traditional regional spit roasted goat)
Las Pampas (Argentine)
San Carlos or El Tio (both Mexican Traditional)
HOWEVER, near the hotel I would recommend La Valentina. There's one in Valle and one in Barrio Antiguo, so make sure they take you to the one that's in Valle. It's a Mexican traditional, which means mostly meat (they bring it tableside so you can choose) and it's moderately priced. There's an Italian restaurant (Italianis) nextdoor so if you get there and decide you'd rather opt for Italian, you have a choice.
On the high end side, the Hotel Quinta Real has a very nice restuarant that is on par with restuarant prices in the US for fine dining (about 200 for two with wine and dessert). Not sure if the conference budget will cover that.
If you want to go to the oldest part of the city, it will be less than $10 cab from your hotel and go to Ianelli, an Italian restaurant in Barrio Antiguo. It's very quaint and also reasonably priced.
After that, definitley head to Havana, a bar that's also not too far away. The restaurant can call you a cab if you need to cab it from Valentina. It's kind of upscale (business casual), but will be a great place for a group after meetings all day.
Okay, better get back on topic - AA in MTY or the webmaster will delete us.