We just bought a house. Let me tell you, I don't know exactly what the average home price is where you live, but let's just say it's $450K+ for one of these 3,000 SF houses that are brand-new. Your mortgage is going to be above $3K/month (including insurance, property taxes, PMI, etc - really, look into all of that). Also, as you know, new housing developments typically have tiny lots, so you will lose that big back yard (unless you can buy 2 lots side by side, but then you're looking at an additional $150K or more onto the cost of your mortgage).
In general, new housing developments are almost never worth the money. Truly. The price per square foot is outrageous when compared to the cost of buying a slightly older home and just remodeling it to your taste.
So my suggestion would be, yes, go ahead and look for a new place, but no, don't buy brand-new. Buy something that's 5-10 years old with a layout that works for you, and remodel it to suit your taste. Generally a little paint and maybe some different flooring, and you can really make it your own for a fraction of the price of building a new house. Houses that are in this age range will be just as energy-efficient. If you're not in a big hurry, take your time, look around, and you can probably find a place with a larger yard and a better layout that will work for you.
Another thought - you can probably keep your existing house and rent it out for a profit. If you need that equity in order to put a down payment on a new house, maybe look into taking a 2nd mortgage out on the house in order to do that. If you have a 15 year mortgage with, let's say, 12 years to pay on it, you can rent it out, the tenant is covering the cost of the mortgage for you, and in 12 years, you own the house free and clear, and you'll have residual income every month. Just a thought!