After playing Rock Band at A&JP, we thought it would be fun to do together, and klik wanted to get back into doing something with music semi-regularly again -- so Rock Band could serve as an easy way into that. But the Wii version doesn't support downloadable content, doesn't support play over network, or combining 'song packs' with the game itself.
The PS3 and Xbox360 versions do support that -- so given the choice, I'd go for the PS3. Some research turned up that the machines cost around EUR 300 -- kind of much, and how bad did we want this anyway? So then we turned to the internet to see if there were any second-hand machines available for what price.
One of my searches turned up a second-hand machine, just over a year old, with 4 games included: FF13, Enternal Sonata, Metal Gear Solid and Street Fighter. The first three games are games that I would be interested in anyway -- and I could get the whole bundle for EUR 250. And it was only a 15 minute drive away from us. So I contacted the seller, and after some fiddling to get his account details (which also contained his credit card number...) removed from the device, we packed it up and took it home.
So far, we have played Eternal Sonata the most. The battle system is turn-based but with elements of an action RPG, and has a coop-mode, so we have been playing it together. Lots of fun.
Now we just have to look for a nice second-hand set of Rock Band instruments.