I think what you need to consider is that the ball joints wear fairly quickly, in around 3-5 years, and to replace these requires the whole suspension arm replaced. So you are likely to have to replace the whole arm relatively soon anyway so any work on the bushes alone may be a short term job. I think if you want to improve the handling ARB's are a better bet (see thread on the holy grail), and possibly geometry, since most of the cars are not set up well. I would question why you think this is a job worth doing? It is also worth noting there is a significant documented issue with cracks appearing in the suspension arm around the bushes, and i would worry about that, both now on your car, and also as a possible result of changing the bushes, all of which would put me off changing bushes.