I'm not gonna comment on the main theme of your post, but as to it not giving you the boost sometimes, usually that's because you didn't complete the barrel roll in time, there's usually an audio cue to let you know that your ship has hit the deck.
your mileage may vary, but I've found that to be the only reason for not getting the boost myself. what I find a bigger problem is the times when it simply refuses to initiate the barrel roll
