You might want to become familiar with at least some of the Ten Minute Math activities, either in the back of each 4th grade unit or by getting them all in one book from (I think) Dale Seymour Publications. These activities take the place of the classroom routines you are already familiar with in grade 2 such as Today's Number. Some of them can stay around all year in a math center while others show up just during a particular unit. The students coming to 4th grade should be familiar with some of the Ten Minute Math activities since they are also used in the 3rd grade units.
The Geo-Logo program is the same in grade 4 as it is in grade 2. The activities in the software are not the same but you will be able to become familiar with them quickly if you used the software in grade 2.
A few teachers in the district where I work have moved up or down from one "Investigations" grade to another and said that it was an eye-opener to really experience what came before or came after in the program. They said that the move helped them see the connections between what they did in the one grade and what they were now doing in their new grade. They also said that the move was a bit easier since the teaching philosophy is the same throughout the program.