Should the space above the cabinet be finished somehow all the way to the ceiling? Especially if there are 42" cabinets and 9' ceilings? There is not much space at the top of the cabinet to merchandise, so the space is empty.

Susan,
Your proposed setup with 42" cabinets and 9' ceiling would look great. We design kitchens without installing cabinets to the ceiling all of the time. The look is great especially if you add above cabinet lighting.

There is always the option of some sort of molding going to the ceiling. We do alot of that...stack 2 or 3 different types to reach to the ceiling. your 9' ceiling with 42" high cabinets is alot of space to fill with molding...but we have done it and it looks amazing!!!