Durty, the insight on what you like about your other guns is helpful. The .223 doesn't shoot as fast and flat as a .22-250, but it is still pretty flat. Where I like it hunting is when I am shooting prairie dogs a couple hundred yards out. I can use the dots in the scope to estimate range based on the standing height of the p-dog, then take shot and watch the bullet hit because a 20" HBAR upper with a weight in the stock has 0 recoil. If I am off, I can immediately correct for the next shot a fraction of a second later, before the target has a chance to move, without moving my body to manipulate the action. I have hunted prairie dogs with a bolt action (admittedly never a .22-250), and my success rate is much much higher with the AR.
I wouldn't buy one used unless I knew the seller pretty well... It is up to you on that one, but make sure you do your research to make sure what you are getting is what you want, and is really cheaper than buying new. If someone bought the gun in the last few years, they may be trying to recoup the ridiculous amount of money they spent on it. Prices of AR parts have come down in the last year or so, and I have seen a lot of used ARs with asking prices that are higher than what I could build it for out of new parts.
EDIT - I agree with the comments above - no gun purchases for a year?!? What if you sell something else that is taking up space in your safe? Did she agree not to buy any unnecessary fashion accessories, shoes, purses, or accent pillows (make no mistake my friend, those accent pillows cost more than you think)?