I'd love to see pictures of the room. Can you post some?

You can use an area rug under the smaller space, that will ground it and define the area. You can tie the 2 areas together by having some sort of color pulled from the rug and use it in the dining area somehow.. maybe in the dining chair's cushions? art? accessories?

Yes, please, pictures. YOu know how we are.

I am trying to do the math on this. LOL

Where do you enter the room? I think I would want the window with the seating area closest to where you enter the room, if you enter at one end.

Will the table be extended all the time(13 ft), or be at the just over 7'length most of the time?

Am I correct in assuming that the room is 27' long, so the fireplace and credenza are on a long wall?

Here is what I am thinking. First, that pix would help. :-)

Second, even with the table open, allowing for three feet at either end of the table fully extended leaves you with a space at one end of 8 x 13 feet, which is a decent space for some seating. Plus, my inclination to balance the credenza and mirror on the one side is a tall bookcase/displace cabinet on the other. That would tie in nicely with the seating area, giving it the sense of a library space.

If the floors are wood, a rug under the table and one in the seating area would help, but the rug under the table is dependent upon how the table will be sized most of the time.

Thank you all for your thoughtful comments. I'm new to Garden Web so I have to figure out how to post pictures. The room is quite a mess right now with all sorts of furniture scattered about and even my bicycle which I intend to take downstairs to use as a stationary exercise bike until September or whenever the weather cools down again. This room is part of a more extensive remodeling project so even when the bicycle goes, there may be other stupid stuff in the room periodically. The house is a one-owner built in 1962 and never ever updated. We've been extensively updating both exterior and interior since 2005. I truly appreciate getting the feedback.

I agree with bumblebbes suggestion to balance the area with rugs.

Offhand, without pictures, another possibility would be to float the credenza between the two "areas" right angles to your fireplace wall; having it function with a dual purpose sofa table and credenza, by having the back of it butt up to a sofa and the front face the dining room side. This would allow you to create more balance on the fireplace wall.