Eibach sway bars are are great upgrade, however the sways and links will really have little effect on low speed straights.
Same with compression rods even if the ball joint or bush is worn, unless the bush has fallen out which would also give you a loud knock on uneven surfaces.
First thing that I would be looking at is your tyres mate, however I am struggling to see how you can have the issues that you have described whilst travelling in a straight line at 30 mph.