Quebec City is wonderful and totally worth seeing! You will definitely get a taste of Europe and a great history lesson. It's very very touristy though (think medieval village crossed with Times Square). However, Quebec the province in general has a lot to offer if you were interested in a road trip and a little more variety. For a shorter trip (3-4 days), you could see Quebec City and the Eastern Townships, which are gorgeous. If you have more time (5-8 or more days), you could start in Montreal (which is both very modern and very old) and work your way east to the Saguenay or the even Bay of Fundy.
Where are you coming from? And when are you thinking of coming?
Happy mumma to my boys Henny Tom (Nov 30, 2008), Arlo Odie (Oct 5, 2010), and baby SISTER! due mid-Dec 2014.