Well, we've gotten relatively good at making positrons, even using them in relatively everyday life (PET scans if anyone doesn't know), but positrons are orders of magnitude smaller than anti-neutrons and anti-protons. Making actual anti-atoms isn't something we've done a lot, and it seems to be extremely inefficient at this point.
Fission seems like a significantly better option for energy research. >>853> to collect antimatter out in space
Where do you suppose we'd get non-trivial amounts of antimatter in space? I've not seen anything to indicate that could be a valid source of it.
Also, your plan doesn't really seem that efficient, with the creation of rockets to send things in space, which is definitely nowhere near cheap, and probably more than we would get back.