I'm not sure if quality of sleep is determined by the worth of personal quarters, or by the quality of the bed, or both. If it's only the first thing then there is no point putting beds in dormitories and my gnomes may as well have straw beds.
1 Answer
According to the wiki the quality of sleep is only determined by the worth of personal quarters. Beds are obviously worth more than straw so they are more desirable than straw beds in personal quarters and directly effect the worth of the room they are in but are not the sole determining factor of personal quarter worth.
http://www.gnomoriawiki.com/wiki/Personal_Quarters#Personal_Quarters
http://www.gnomoriawiki.com/wiki/Bed#Beds
So yes a bed in the dormitories will be useless since it seems sleep quality in a dormitory is fixed.
Something you can do is build beds anyway since you will need them eventually and 'store them' in the dormitory until you have personal quarters to move them to.