IMO build a solid 1.2 wall and then if tyou want put someting on top of it but IMO a bookcase type wall would not be very attractive there ,

That type of baluster is quite skinny and more fragile than a heavier weight one. So if you replace it make sure that you use a sturdier baluster. Or a half wall with the same type of wainscoting as your walls.

Half wall for sure!!

I agree with the half wall. Makes it look more compete as a seperate room. BTW, love your round table and natural chairs.

I would suggest a half wall - but if you like the look of balusters, then go with a more meatier newel posts with metal spindles anchored into a bottom plate such as this.