Never been to Dallas, and looking for an upscale hotel that screams "Dallas" with immediate walking access to an old area of architectural and historic worth. Thoughts, please.

Hmmm...I'm not sure what "screams Dallas" means exactly but I'd suggest the Melrose, a historic hotel in the Oak Lawn area. Alternatively, the Mansion on Turtle Creek or Hotel Crescent Court may fit the bill. (Please remember that most of Dallas is not historic!)

"Old, architectural, historic worth"?
Not sure where you'll find this in Dallas, but it won't be within walking distance to a hotel you'd be staying at.
And "screams Dallas" is a tough one. All the best hotels in Dallas are virtually transplantable. They'd fit nocely in LA or New Orleans.
The Mansion on Turtle Creek has by far the most charm and atmosphere IMO. We've stayed there for a couple anniversaries and weddings. But it doesn't even "whisper Dallas". It's just one of the 5 highest rated hotels in the US without screaming anything.

dallas isn't really known for either architecture or history, unless you count the sixth floor museum, which commemorates the assassination of JFK. (sounds creepy but it's interesting)

That said, above suggestions are about the best there is. you also might think about the Magnolia, which is kind of a boutique-y property; or staying in Fort Worth (which has better museums and a more lively downtown, well, at night anyway) at the Ashton, which is a boutique renovation of an old downtown office building.

If you want to stay downtown, I agree that a great boutique hotel is the Magnolia. My entire wedding party and guests stayed there. Very cute, nice hotel.