Yeah, KM7's multiplayer isn't all that restrictive. It's the standard kart with a Shy Guy if you do it via Download Play, and the download players don't get the actual course music, but you have the choice of all the courses and any players who actually have the game have access to everything.
The thing is that DS games are a more viable multiplayer option for me right now, since we have a lot more DS systems in the family than 3DS. Still, my brother's having a blast in Time Trial mode, and I've heard Mission Mode is really great (haven't played it yet) so was probably still worth the money.
And yes I agree MPDS Download Play is fantastic, it's a shame that newer installments have been gradually dropping that
Sadly.