Nintendo is targeting a new market, sure, and it works in specific incidents. But there is still no cold proof (IE, Senior Citizen gaming on a percentage rise because of Wii) if it's successful or if it's a failure.
You're right in saying it's not a sucess in the senior citizen market, but it has started making a positive growing interest within that market, something no other console has specifically tried to do. Wii Sports, Wii Play, and soon Big Brain Academy are fairly strong and positive steps towards establishing a lite gaming community. It's a market that the 360 and PS3 are totally ignoring, so competition is limited to the DS of all things. ;)
Will it fail, do decent, or be a resounding success? We won't know for a while, but you have to admit it's taken some good steps in the direction of appealing to them. If it only adds 2-3% of the Wii's user base, that's still another 2-3% that the 360 and PS3 are unlikely to ever add to their users due to the interface, and probably just a few more software titles sales that wouldn't exist otherwise. And don't forget the Wii encourages more in-person social interaction than the PS3 or 360, which is something that the retired 55+ age group seems to enjoy far more than us whipper-snappers. :)
I don't have no numbers, but I wish I could bet money that at the same point in any other console's life over the past few generations, that the Wii has the highest number of "first time console owners". I'd even say at approaching 6 months old since launch comparison it's the fastest selling console yet to the 55+ age group. ;) I think it'd be a pretty safe bet. And I'd also bet that those numbers will continue to grow fairly quickly until Fall '07 at the earliest, I try to be conservative, so I won't guess beyond there. :)
Note : I do enjoy John Lucas's posts, but I do tend to find them a bit too positive for my taste. To each their own though. ^_^
Nobody is crazy enough to accuse me of being sane.