If we see 4.5% rates with some YSP, you bet your bottom dollar it will be a boom. Forget about the cashouts and forget about self employed folks without decent tax returns, there are plenty of other folks out there that bought and refi'd at 5.75% on up that would love to get some of that 4.0 to 4.5% money....after all, we'll be selling long term savings, not short term payment and time to recoup new closing costs....
There will be plenty of FHA streamlines, VA streamlines, and good ol' Rate and Term deals where the customer gets $2k in their pocket and skips 2 mortgage payments!
So the answer is YES, most definitely YES, the low rates (as long as their's some ysp in it and are in the 4-4.5% range) will spark a refi boom! And YES, even with rates in 4.5% to 5%, we will see a lot of refi's as well....but maybe we'll call that a refi bang, not quite a boom.