If you are after improving your suspension the best idea is to find out what is wrong with what you have got first.
If you are in Bristol go to somewhere like Protyre and get them to do a free suspension check and tell you what is wrong.
Then decide where you need to spend the money.
A good home check for shock absorbers is to push down on the corner of your car (x4) and release, the corner should pop up and bounce once, if it bounces two or three times your shock absober will need replacing.
Changing anti roll bars will not cure problems with defective springs, shocks, or rubbers. Same goes for changing any of the other parts, if you change the wrong part it will not fix problems with other parts. Anything you change in the suspension will have an effect on the other parts of the suspension.
If you are after improving the suspension for the cheapest price, get it all checked and replace anything that needs replacing with standard parts. If you can afford more money first get it checked to see if anything needs replacing then go for the best suspension you can afford either coilovers or struts and springs. Remember the lower you go the harsher it will probably be.
Paul