I took 4x shield boosters and engineered them with 'resistance augmented' (Grade 5 obviously because I am not a Sunday-flyer)
I took enough materials for 24 attempts.
I consider anything above 75% on the major stat to be good.
I consider anything with a power reduction secondary to be even better.
I have discovered that accepting any roll and then rolling again tends to be far more rewarding than attempting to get a good roll on a virgin module; in fact the statistics will gradually creep up and up if you keep rolling and accepting any improvement. This would appear to be true because the outcome bars will alter based on what is already on the module. A maxed module will therefore have no blue at all, and it would take a miracle to get an improvement.
In my experience (my main ship is finished 100%) it doesn't take more than six rolls to get a decent result, and anything up to ten or fifteen after that will improve the result you accepted. Keep going for another ten or so and you might end up with a magnificent result, as this image shows:
*but damn that booster is so weak, even a photon grenade could take it out...