Plan to take cruise. Is it necessary to pay $100 more to pre-sel

Two options. One is to choose the guaranteed stateroom for lower price, but will know the actual room at the check in date. Or pay $200 more to select the room now. Very similar to those tricks used by airlines during the booking. Can anyone share their experience whether it is necessary or not? Since it is an interior stateroom, I do not think there is big difference between floors and locations. My only concern here is we need two rooms and maybe it will be located in different floors and far away between each other. First time to take cruise. Any feedback is highly appreciated.