Depending on where you will be in Arlington, there are a ton of decent-enough places for everyday dinners, although not too many are spectacular. The corridor from Rosslyn through Clarendon and on to Ballston is heavily populated with young professionals, and lots restaurants mirror that. Heavily populated, solid food, and plenty of bar area. And there are 'upper crust' chain restaurants, like Cheescake Factory and Las Tapas. There's also a small group of Ray's restaurants, starting with Ray's the Steaks and Hellburger. Ray's the Steaks is known for being a no-frills, top-flight steak house. Costs less then Ruth's Chris, etc., and argueably has better steaks. The atmosphere is a bit, well, basic, but that's why they can offer lower prices.
And if you will be staying closer to Shirlington, there is a strip full of restaurants (again, mainly so-so), with a really good Thai place, and a 'modern Italian' place called Extra Virgin that makes their own pasta and sausage. Out of the two, I'd go with the Thai though. Less expensive, and consistantly good.
The Omni kinda exists in it's own world near the National Zoo. It's a large compound, but right outside the end of the main drive is a strip loaded with restaurants. Lebanese Taverna is pretty good, and has some ligher fare that should do well for lunch. There's also a sushi place (I don't know anything about it, though). But as close as these places are, it may be tough to walk there, get seated, eat and return in less then 1-1/2 hours. Of course there are places to eat in the Omni compound, and if your lunch breaks are short you may have to make do with them.
The Omni is also less then a mile from an area called Adams Morgan, which is a mixing pot of ethnic restaurants from all over the world. Easily over 50 places. I don't have much to offer here; you'd be better off doing some Internet searches and seeing what types of cuisine interest you. Most of the places are pretty small, and as a whole they tend to be less expensive then restaurants in some other parts of town.
But for that night you want to treat your relatives, definitely take Travis up on his offer. Do not pass go. Do not collect $200. Make setting this up the first order of business in your trip planning. The passion he and his team have is infectious.
They have a pretty extensive wine list as well. Most were $45-65/ bottle, although there are soeme higher and lower.
