The way I have done this is in the past is to make the falling objects have a 'bullet' behaviour attatched. Set up all the parameters so that the objects fall the way / direction you want them to, but under the 'speed' or parameter, make a variable called 'Speed'. (So under the events, have an event that is something like "On 'object to catch' created" set speed to "speed". That way, you can manipulate the speed at run time through algorithms that are fairly simple, such as "If score > 250, speed = 250"
If you were going to event that, (and assuming your score is a global var), you'd make an event under system;
"compare variable" and define what range of score you want for a particular speed (e.g between 250 and 500), and then have that even set the variable 'speed' to the speed you would like.
Hope that helps and isn't too garbled!