You don't get anything different. Since getting all four of the evidence just decrease the chance of you choosing the box of evidence that points that Donald and Goofy are the culprit trying to steal the Queen of Hearts' heart.
Here in the Lotus forest you will meet the mysterious, very cool looking Cheshire Cat, but he tends to talk in riddles, so he can be more annoying than helpful. He still is the coolest character though! There are four pieces of evidence. You only have to find one, but it is very beneficial to find all four of them. Start by searching the small alcove to the right. If you walk straight forward from the door that you came in, you will walk past a red flower, and the alcove is right there to your right. There is a small pink chest containing FOOTPRINTS, which is one of the pieces of evidence (footprints in a box?). There is also a Trinity mark here as well. Use it to obtain a POTION, an ETHER, a TENT, and some MP balls. You can also give the flower a Potion for a HI-POTION and more MP balls.
There are also a couple of red flowers, the one near the entrance, and one on the other side of the forest. Give them both Ethers to get a CAMPING SET from each one. Do this only if you have some extra Ethers. These flowers also spit out HP balls.
Back in the alcove with the Trinity mark, jump up the mushrooms until you reach a door on the side of the big tree. This will take you back to the Bizarre Room. You will land on the fireplace next to a chest containing the STENCH. Just two more pieces of evidence!
In the back of the forest, past the second red flower, are more mushrooms. Jump on the little one, and then jump on to the mushroom to the right. From here, you can see another evidence box. Jump across to it, and open it for an ANTENNA. Look to the corner of the room to see a blue chest. The jump to the ledge is really hard, but Sora will grab on if you jump at the last possible second while running off the edge. The chest here contains a THUNDER-G. Back at the bottom, jump on the small mushroom again and then jump to the left. There is a chest here that contains DALMATIANS 16, 17, and 18. Congrats!
Back at the entrance, look for the other yellow flower next to the fake lake. Give this one a Potion to grow bigger. Step on the nearby stump (right next to the entrance, you'll get the message "see ya") to raise a platform, and then head over to the big tree in the middle of the area. Choose to "take" the seed after examining it, but leave it on the ground. Hit the tree to change its direction, and then eat the seed to shrink again. Back in the alcove where you found the first piece of evidence, jump up the mushrooms again and follow the platforms to a new opening on the wall that leads to the Bizarre Room.
Be careful when you land! You don't want to fall off. Use the first person view to spot the last chest. Carefully jump across to it, and open it for the CLAW MARKS. The Cheshire Cat appears to give you BLIZZARD magic. Yay! Now you can blast those pesky little mages out of the air, and get Tech points for it! Now jump back down and head back to present the evidence to the Queen.