While 9' ceiling give you a more spacious feel, particularly in a smaller space, over 8' ceilings, I find 10' ceilings completely change the way you decorate and illuminate the occupied space. You suddenly have much more storage space above your bookshelf. Changing light bulbs require a real ladder, not just a chair. Artwork can be larger and positioned higher up to better balance your 'canvas'. Lighting requirements can change in terms of angle of spot lights, intensity, frequency/spacing, etc.
Of course, these are all minor factors to consider for a much more spacious feel of your living space. Small spaces suddenly feel airy!