Thanks very much - I was looking at driving there in a day, staying overnight, having half a day sightseeing and driving back - does that sound viable or is there enough to do to warrant a whole day there ?
depends... you can go over the falls (in a plane rather than a barrel), under them, up to them on the Maid of the Mist, behind them via some caves...
Personally I'd stay there for the second night, if only because driving 600 miles in two days is tiring (though maybe you've got someone to share it with?). But yes, you should be able to do it in two days.