I'm with funcolors...ceiling white is an abomination! In most rooms, an untinted white ceiling sits there over your head like a piece of posterboard, and makes you feel as though you were in a shoebox with the lid on. In our previous house, I used a nice warm gray in our library, which had substantial crown and cabinetry in cream, and I painted the ceiling a very pale peachy pink. Not noticeable unless you looked at it, but it warmed the whole business up considerably. And I used eggshell finish, because I wanted a very subtle sheen in that room. Whenever the ceiling surface is in very good condition, I prefer eggshell...but it will make textures and flaws more noticeable. Rooms with high ceilings and no crown look wonderful with the ceilings painted the same color as the walls (the height of the ceiling mitigates the flop angle). Pale pale blue can look lovely with camel colors. Green, I think, is always a little weird, because the sky is almost never green (unless you're about to take an unscheduled trip to Oz...). With green walls, a very subtle pale gold tint is nice. And if a white ceiling is desired, matching the trim color is the way to go. I usually choose cream ceilings with red or terracotta walls, because red is very reflective and will tint the ceiling with reflected light, and the yellow in the cream keeps it nice and warm.

Cove molding is a variety of crown molding with a concave profile. I don't find that it makes the ceiling look higher; some experts say that by drawing attention to the ceiling, the ceiling may in fact look lower. To counteract that, paint the ceiling a lighter colour than the walls. Crown molding does make for a smoother transition and is characteristically used in more expensive traditional homes. Or in homes that are aspiring to a traditional look. Plaster Cove Moulding Handpainted Detail on Plaster Moulding Crown mouldings are made of polyurethane and other foams, wood, pre-caster plaster and cast-in place plaster. Here is a link that might be useful: Balmer Architectural Mouldings

An inexpensive way to get a hefty base board is to use 1"x6" boards and a 1 3/8" base cap. It will be nearly 7" tall and it's an easy install. I would use a 1x 3/4" base shoe with that but that's a matter of taste. The base board provides the visual foundation for the room. As such, it's the one piece of molding that can be out sized compared to the rest. Get some of the material you intend to use and lean it against the wall in your room and see if the size works. If you feel that your existing case should be larger a backband is an inexpensive way to add some size. You'll need a table saw for this but if you have one or can get to one it's easy after that. Take some 1"x6" and cut it into strips 1/8" wider than your case is tall. Sand the banding and break the leading edge with sand paper. Install it around the outside of your exisitng casing. When it's finished you'll gain 3/4" in width and extra depth. Visually it will appear even larger. I've never used foam crown but it could work. The trim in commercial buildings is commonly glued on foam. Once it's painted who's to know or care? They used to make it out of plaster even cement and nobody cares. I can't imagine how your crown molding is going to get dented. If you try it report back on how ti went; I'd like to know.

You've got several problems. If you buy more of the same crown from your cabinet company, you'll still have to deal with the gap above the corner cabinet. If you raise the existing crown to the ceiling, it's very unlikely you'd find unpainted crown that matches it's size and profile, plus you'd then have to deal with a gap between the cabinets and the bottom of the crown. Here's what I would do. Choose the new crown mold you want for the rest of the room and measure it's height (how far down from the ceiling it comes). Make a mark on the wall at that height, then use a level to transfer that height to the stained crown and mark it. Then, trace the old, existing crown's profile onto the wall with a pencil. Now you have a mark where the bottom of the new crown will intersect the old crown, and another mark where the old crown will have to be narrowed to fit underneath the new. Carefully remove the stained crown from the corner cabinet. Next, build a frame above the corner cabinet that's the same height as the new crown, and that extends beyond the cabinet to the point at which the new crown will intersect the old. Now, install the new, painted crown around the kitchen and across the new soffit. Last, run the old crown through a table saw and cut it down so that it fits underneath the new crown. With me? This is a tough one to visualize.