I've slightly revised my ideas... These are all the spaces I want:
Blue Space - Gain 3 coins
Red Space - Lose 3 coins
Green Space - Trigger a board-related event
DK Space - Causes DK to appear and do something good
Bowser Space - Causes Bowser to appear and do something bad
Duel Space - Summons Toadsworth to start a Duel Mini-Game
Friend Space - Summons Tumble to give 5 coins to two characters
Banana Space - Summons Diddy Kong who starts a Banana Mini-Game (replacement of DK Mini-Games)
Graffiti Space - Summons Bowser Jr. who starts a Jr. Mini-Game (replacement of Bowser Mini-Games)
Comet Space - Summons Rosalina who starts a Comet Mini-Game (like Battle Mini-Games, but no one has to give coins into the pot)
Lucky Space - Sends you to a special area of the board with a free Star
Portal Space - Warps you to another Portal Space on the board
Star Space - Lets you buy a Star
Orb Space - Gives you one free Orb
The trick is: DK Spaces and Bowser Spaces automatically alternate with each other when one is landed on. They can also switch with each other via an Orb. The same goes for the Duel Spaces and Friend Spaces.