When you get fastpasses you need to look at how much the fastpass will benefit you. I think that some fastpasses are more useful then others at different times of the year depending on how the crowd levels are.
Space mountain will run out quickest and fastest. Also, the space mountain fast pass allows you to skip through the huge outside line of people (usually the CM will make the crowd wait for awhile so you can easily skip past 60 people).
Indy fastpass only allows you to skip by the people outside then the CM will take your fastpass and you will join the stand by line as soon as you get inside. I have never seen the line outside for this ride in the off season. The only time a fastpass is needed for Indy I believe is if you are going during the summer when it's packed.