Nothing will affect the feel of your house as much as the quality of the light. If you can at all swing it, keep your divided lights. Looking at your photo, those windows are gorgeous. Can you place glass on the exterior? I have some lead light windows in 2 locations. I made new frames with the leaded old glass on the inside and plain glass on the outside. While not as weather-tight, it's much better than single glass. While not as neat as your present windows, the new windows that have the interior and exterior lights with the spacers between the glass also look great and are at the present standards for energy efficient. We live in the PNW and used Milgard; less expensive than Anderson and Marvin, but so far I'm very happy with them.

Check with your realtor about spending any money on an update. Tidy up the stuff in the corner, put the sofa next to the fireplace facing the view, angle the chair near it, and let the next people decide what to do with the space. Some people will love the wood, others won't, but don't try to guess. You could spend a small fortune on new flooring only to have it ripped out as people make the space their own.

I understand wanting to keep the views from as many rooms as possible. However, how much time is spent in the bedrooms? And is the view visible the majority of time one spends in the bedroom? Consider that the most restful, secure sleep is obtained when the bed is placed opposite the entry door. That is not possible in any of your current bedroom layouts. Perhaps you should consider single solid glass French doors or windows flanking the beds opposite the doors rather than the large windows you show on the plan. Choice of doors or windows would be based on accessibility to a deck. I assume bedroom 1 and the office/bedroom have built-in bunk beds. I think the deck between the family and bedroom 3 seems inaccessible and a bit of a waste, and I wonder how one gets outside from the kitchen with the trash, etc. Do you have no plans to garage the vehicles?

I already have a quote to do repairs on my Windows but the additional money would allow me to purcase two new Windows in the south side of my house with new double glazed Windows which would add a huge increase in value, & additional warmth in Winter, which is in my mind, money well invested.