i suggest one of two things:
(1) scrap the random angle function altogether, and let the amount of damage done by a direct hit be adjustable so that at easier levels, less damage is incurred by each direct hit (this will achieve the same effect of your random angles, because in either case, the hit points of the player are preserved at easier levels) or
(2) don't add a random angle to each frame or cycle of the routine in which the ship determines which way it needs to face. this is what cause the wiggling, stalling and silly look. instead, let the random function come in every fifth, or tenth or hundredth routine. this will make the direction seeking seem smoother, and still allow for poor aim at easier levels.