Here is the existing plan (demo).

I forgot to note that the area outside of the kitchen will be dining and a small sitting/keeping area.

RS, I am in very much the same boat --- 4 level split, all brick, LR,DR,K and hall on main level. For many years, I tried to imagine a plan that would repurpose the rooms so that I wouldn't have to do an addition. I've finally taken the plunge and am pushing out the back (only), just shy of 8'.

As for any layout advice, my plans are for the K to be open to a casual LR and a separate DR. So, my DR will move to the front room (currently LR) and once the back wall comes down and space is added on, I will have the K and LR as one large-ish room. In the kitchen, I desire table space, so I'm adding a window seat along a portion of the back wall, followed by french doors that will lead out to a deck. (I'm envious of your plans for a screened porch!)

I will be watching this thread with interest and excitement, as I move forward with my remodel. Good luck!!

Since no one has given you any feedback yet, I'll take a shot...

So you have what people call a barrier island. That means for the normal kitchen workflow you would have to walk around your island.
If you read this thread, you will see the main problem with your workflow:
http://ths.gardenweb.com/forums/load/kitchbath/msg111625296905.html
(Maybe this thread should be made sticky?)

To fix your workflow, you could either move your fridge to the wall with your sink or add a prep sink on your island.

Also, through what door do you bring in your groceries? The small door in the kitchen to the foyer seems like it will encourage a traffic pattern through your kitchen. Having more counters/pantry there may be better.

Regarding the powder room... having the guests go through the mudroom to the power room seems awkward and inconvenient. Could you have it open on the other side into the living room (I think that is the living room)? Also, you only need 2 more feet for a full bath. It seems like you have plenty of room to add a full bath if that is something that would be of value to you (it does help resale).

Hopefully some others will chime in and help you out with this one.

Thanks Robin -
I am planning a prep sink in the island (if we go with that layout). I agree about the small entry off the foyer, but the front door is the door we use the most (closest to driveway and our primary alarm is set for that one). The back door is from a fenced backyard.
I had thought about closing it, but don't think it will be practical. I tried to keep the work zones in mind while at the same time keeping the exterior wall as open as possible. The ceiling will bump up past the new beam (in alignment with the bumpout). I may do some research to see if there are any cool/modern half doors/gates - or even hidden doors. But that may be getting a little too crazy.

When we did a major first floor remodel with addition, we ended up moving the kitchen to the former dining space in order to solve the exact problem of walking straight from entry into kitchen.

Also, just like you, we added a mud room space between the new kitchen/dining and garage. I actually am happy that we come from mud room into kitchen rather than dining, and ended up adding a walk-in pantry to the mudroom. You are doing so much anyway, you may want to consider it. We ended up being able to create a much more functional kitchen space and we couldn't be happier with our decision.

As much as I am function over form, possibly the best part is that now when we enter our home, we have a wonderful view out the back windows into our yard rather than the kitchen. I hated walking into the house and immediately seeing the kitchen sink.

Sorry, but I just don't understand the new plan. What are the spaces around it? I am not sure on which side the "front" is. It looks like you are getting rid of both the dining room and the living room entirely or are you only showing the portion of the new plan that is the kitchen area?

I'd move the fridge to the cooktop wall and add a prep sink on the island. Moving the fridge to end of the main sink counter can be another alternative, but I think fridge and cooktop would be too far from each other in such a layout.

Can you turn the coat(?) closet 90 degrees and move it to the other side of the kitchen entry, as much to the left as possible? You can then enlarge the kitchen doorway and maybe move a little to the right, so aisle b/w the cooktop wall and the island wouldn't be right across the entry. That may encourage people to use the back of the island, instead of going through your prep/cooking zone. In case you need additional storage, I think you can add shallow pantry cabs on the DR side of the entry.

For mudroom+bath area, moving the porch(?) door and DR entry closer to the bath may be better. If you can't move the porch door, then maybe you can add another entry to DR closer to the bath.

For the aisles, if they are from edge to edge of counters or handle of appliances, the aisle b/w the main sink and the island seems fine to me. I would consider a larger one b/w the bottom wall and the island, and 42-48" for the cooktop-island one.