We got an old Wii for Christmas this year. It was $50 at Game Stop with a one-year protection plan and one remote/nunchuck. We added two more remotes and a few games and I think we spent around $150-$170 altogether vs. $400 for a Wii U with three remotes and no games. If we later want to move to the Wii U, the remotes will work with that, so we will basically not be out any money there. I was concerned that at the ages we have they would be outgrowing the Wii/Wii U in a few years wanting an XBox or PS, not to mention the struggling of the Wii U (was rumored at the time to be on the way out, but not sure now), so I didn't want to invest in the Wii U.
Anyway, they have enjoyed it plenty. There are tons of older games that are new to them. A few they wish they had (Lego Movie and Mario Kart 8), but not too many.
Mama to three boys ('03, '05, '07)