Yes I use the Rubber "O" Rings as well to great effect. I started using them on the shock mounting balls before snapping on the shocks and they work a treat. My shocks dont twist from side to side any more.
To be honest my 04 doesn't really have much slop at all. Especially compared to my TA03F which is full of alloy parts including the steering assembly.
Changing to the alloy steering arms as far as i can see will make no difference to the "slop". I found that what little slop there is in my 04, is generated in the ball cups and replacing them often will help keep that to a minimum.