I've rollered a few cheapo motors with good results and a definite improvement on what they were before, but If you roller use a mini roller and make sure you get good quality rollers and not cheap ones, they aren't that expensive really and it makes the difference between a good job or not, I don't think the paint matters too much, I've used all sorts.
But the prep is the key, a badly prepped surface will never look good whether sprayed or rollered.
I would definitely spray it.