One option is to paint over the beams with simple white.

Are they support beams or just for show? We took ours down and it opened the whole room up. If they are supportive, paint them the same color you paint the ceiling so they disappear. Also, get rid of the outdated railings and spindles too!

Also get rid of the built ins and whitewash the fireplace.

Painting rough cedar is not that easy as it is an oily wood. It absorbs lots of paint and can bleed through. I'd get rid of all that is not structurally necessary, including the shelving units if they are cedar as well, and go from there. You may want to put a lighter wood, like a pine, between the ceiling beams if they need to stay. Look at some Houzz photos, that can look pretty nice.

HI - I hope you are going to remove the fence room divider -- I am certain none of this is supporting , just decorative for lack of a better term . Leave the beams the dark and apply some TG pine or flooring wood between and then white wash it . This will be an nice updated accent to this 70's house . I don't see a mess just an opportunity or potential to respect the age of the house yet up date it for todays life . Doing anything in the way of painting or re moving the book shelves , depends on what your décor plans are and what ,if anything your planning on doing with the fireplace . What is behind that bookcase /fireplace wall ? If it is possible to open up the space around the fireplace so it is more free standing then re -cladding in a veneer stone or tile . I would be interested in what plans you have for this house .

I painted my rough beams and added car siding (I didn't know what it was but Home Depot did) between. We put some insulation up first and it made lots of difference in our utility bills.

From the picture, either its a perspective illusion, or it looks like the room in the foreground has a drop ridge compared to the ridge in the background room. If that's the case, that open frame is a support for one end of the existing ridge in that room. Don't go knocking any part of it out yet. That beam looks dimensionally too thin for that span if you remove the posts completely. If that's the desire, check with a structural engineer. You could also go to your municipal building/planning dept and ask if they have a prescriptive beam span chart to reference for a rality check. If you're not working with an experienced builder or framer, I wouldn't go DIY on that.

If the posts and beam stay. Custom post wrap and see-though bookshelves 36" high on either side with a nice wood finish. Carry the new wood finish up onto the the overhead beams. The wood wrap will kill the re-sawn/rough-sawn cedar look with an updated smooth finish.

Leave the beam as is. Looks rustic. But remove the lower part it will give the room a much more updated look and open the room. Put in wood floors not to dark. Of course update lights. If remodeling recessed lights in ceiling would help.

I would update fireplace too. Get rid of bookcase not needed. Reface fireplace. With a river stone if going a cabin, rustic feel. Or stacked stone if going more modern. Take it to ceiling. Beams gives room character.

Need an Engineer or licensed builder to look at it all. Let us know what they say? We like beams.

Looks like you need to add a few more beams on the other side of the divider gate. It could be a beautiful room as per Lefty47 suggestions.

Chookchook 2 is right again. Have a professional look at it first, and while you are at it ask about good insulation. Only get rid of the bookcase if you do not have enough books or an interesting (art) collection. I love bookcases and have four of them. Good luck and I hope you keep the Houzzers posted with your progress !