Going to see the Grand Canyon on a day trip from Vegas would be like staying in a hotel Newcastle upon Tyne and wanting to see the Tower of London !
There are plenty of ways to see the Canyon by 'plane, rather than spending a whole day in a rental car...its just plain daft to drive !
However, there are plenty of places to drive to from Vegas, without hours behind the wheel. Vegas is all very well but it would a terrible shame if you didn't take the opportunity to see the countryside around while you are there. Anyway, Vegas can be a bit much after a day of two, as it is "in your face" so to speak. Day or night its impossible to get away from the noise and clamour. Go and see the Hoover Dam...well worth it and you can drive around Lake Mead on the way back :::
http://en.wikipedia.org/wiki/Lake_Mead
The Hoover Dam is amazing. You can go right down inside it and come out at the bottom. Its has to be one of the Wonders of the Modern World ::
http://en.wikipedia.org/wiki/Hoover_Dam
See the Valley of Fire State Park while you are there as well :::
http://www.valley-of-fire.com/
Look at the colour of those rocks !
I wish I was going with you as its been 20 years since I was last there and its unlikely that I will ever go again now. Amazing place.