Personally I like to have my play dates in downtown DC because of the ease of getting around via metro. DuPont is not bad either. And it is a pain o get around in Georgetown.

Have your date take you to Gtown for a romantic dinner, but don't stay there!  It's a nightmare to get to no matter what mode of transportation you use.  DuPont is great for public transit, downtown for drivers (more parking garages).  I think the latter has fancier but still big hotels on average.  You'd want some anonymity!

Georgetown is very difficult to access via car and there's no Metro service there.  The hotels tend to be smaller, more expensive, and don't cater to business--more tourists in Georgetown.
 
Dupont Circle is really downtown; it's defined so broadly that it covers from 15th to 23rd st (about a mile east to west) and from K to T sts (a mile north-south).  There are multiple Metro stops and parking is a possibility.  There's still traffic, but not as congested as Georgetown, for sure.
 
Arlington is on the Metro, just south of downtown and Georgetown, which has a lot of hotels, easier access for Northern Virginians.
 
PM me for specific recommendations, but I don't know much about bathtubs!