If you go knowing what to expect, one week in Niagara Falls is not too much time. Niagara Falls is more like Vegas than the Grand Canyon. Clifton Hill is very much like a carnival midway. Don't go there expecting a National Park experience. Go there and take it as it is.
One thing many people fail to do when in Niagara Falls is to just sit and watch the water tumble over the falls. Don't skip that - otherwise it's just a big waterfall. Watching it flow is hypnotic (many people who have been rescued from the falls have indicated that they didn't intend to go in, but they felt compelled - so watch your footing).
Some of the best things to do:
Maid of the Mist (Canadian side now called Hornblower Tours)
Journey Behind the Falls (Canadian side)
Cave of the Wind (U.S. side)
White Water Walk (Canadian side)
Spanish Aero Car (Canadian side)
Whirlpool Jet Boats (I believe both sides, but for sure Canadian side)
There's also lots of historical sites in the area, lots of smaller attractions (aviary, zoo, movie experiences, gardens, Skylon Tower, fireworks over the falls, etc.).
If you want a "quaint little town", Niagara on the Lake is very popular (similar to a lot of small towns with a tourist-based historical main street).
When you do Cave of the Winds, plan on spending time on Goat Island and the Three Sisters Islands. Nice place for a relaxing picnic lunch as you watch the water flow down the river to the falls. Just remember that even though the water isn't that deep, the undertow can be very strong - follow the signs that say don't wade in the water.
Check the attraction packages for both sides - often you can save a lot of money by buying them.