Thanks for everyone who has taken the time to reply.
I would expect to normally be playing with 2 players and I doubt if I would be playing on-line or wanting to build up a big library of other bands songs.
There was a big difference in the video quality between those two video clips shown and I think I really need to go somewhere and see the kit being demonstrated for real before I shell out my money. In most ways a Wii would probably be best for me because the sports type games are the only other things I would be likely to play as I have zero interest in shooting aliens, but I don't really want to compromise too much on the processing power/graphics.
I think a trip to a shop is in order to see for myself.