Both Old Town Alexandria and National Harbor are within 30 minutes of home, even allowing for traffic congestion. We haven't stayed at NH in a while and parking and points cost are the main reasons why not. We have never stayed at NH unless I could book a 1BR at a discount and upgrade to a 2BR Presidential. To avoid the parking charge, I suppose I could drive to NH, unload the car, drive back home and take Metro to NH. Haven't done that.
If one can book with a VIP discount (or rent from a VIP) and get NH to comp parking in exchange for attending a sales presentation, NH can make sense. The National Harbor development is kind of fun. Lots of restaurants and shops, live entertainment now and then at the Plaza Stage. The Gaylord resort and convention center is nice to walk through although if you've seen the Gaylord Opryland Hotel in Nashville, the facility at NH will disappoint you.
Old Town Alexandria is a better choice if going into the District is why you're visiting the area. Driving into the District is not recommended. I don't do it and I've lived here for thirty-eight years. In fact, the District is not a very safe place. (To paraphrase Former Mayor-for-Life Marion Barry, "Except for the killings, DC is one of the safest places in the country.")
As
@troy12n indicates, there's no beach nearby and Annapolis is about an hour away. The Potomac River is cleaner than it used to be but I wouldn't swim in it, even if there were a beach.