Not a guide by myself or a member of the forums, but Nintendo posted this video at today's Nintendo Direct, and it's a Japanese guide to Coin Rush mode:
http://www.youtube.com/watch?v=3RyfLwp3iz0
It has numerous Gold Mushroom locations you probably don't know about and various additional tips to get as much money as possible, so watch it and see.
There's also a near perfect run through of level 1-A by one of the game's developers showing all the ins and outs of the stage. If you get that level to appear in coin rush, do exactly what that guy is doing, since he gets over 5000 coins from just one level.
http://www.youtube.com/watch?v=3RyfLwp3iz0
It has numerous Gold Mushroom locations you probably don't know about and various additional tips to get as much money as possible, so watch it and see.
There's also a near perfect run through of level 1-A by one of the game's developers showing all the ins and outs of the stage. If you get that level to appear in coin rush, do exactly what that guy is doing, since he gets over 5000 coins from just one level.