Opinions: Buy New Home, or Add on to Current Home?

As some of you know, my DH and I have been working with an architect for plans of expanding our home.

Now that we have figured out what we want, and how big of a house we want I am wondering if we should just move.

Our current home is around 2500-3000 square feet (I put a range in because we will be finishing our current 2 car garage into a two story great room).

The plans for the new addition is approximately 4000 square feet, so the total square footage of our home will be around 7000 square feet.

Now here's what I was thinking...instead of pouring say $600,000 into our current home and making it exactly what we want...should we sell it and just put that money into a larger home (I don't know if it'll be 600,000...I just got that number from doing the average square foot addition multiplied by $125 a square foot for basics, plus demolition work, plus other extras, ie. spiral staircases, curved stairs, etc....)

The other factor...right now we have an amazing view, and it's more than the average waterfront view...our home is close to the bluff, so you feel like you are floating on the water...most newer homes can't legally be this close to the bluff, so they loose some of that 'feeling'. We are also next to a type of ravine so there will not be any building on it because it is protected by the DEC and they will not allow someone to fill it in and destroy it. So, we have an exceptional view that we probably won't find with another home...and our home is almost perched out further than the regular coastline, so it's like our view is more than 180 degrees. We bought this home 5 years ago very very very cheap before the market went nuts, and would make a very nice profit.

We love our home, and I don't think my husband ever wants to leave ...we've been told by our land surveyer, architect, builder that we'd be insane to ever sell and will never duplicate the view.

I don't know, I'd like your opinions.
Thanks