Hard to say without more on your financial situation but:
-You'll be paying more for your house *without* including maintenance which it sounds like will be huge. You'll have to be a landlord, which can suck and be lots of work as well. Hard to put a price on all that, of course.
-The 20 mile (each way?) commute is $20 a day in gas/depreciation/etc so if you're working 20 days a month that's another $400.
-I'm assuming your time is valuable so the commute, if it's a quick one, is an hour a day. Assuming you make $50/hour or so and you're very close to work now, that's another $1000/mo down the toilet.
-The tax savings are nice but unless you're in the 35% bracket or something, it's not going to change the math much. And if you're in the 35% bracket, WTF are you doing financing a 400k house? :)
So financially, sounds like a pretty terrible move. That's not the only consideration, though. If you really love the house and want to live there and you're ok with spending ~$20k/year extra to do so, do it.
-W