As long as it hasn't got play and isn't an MOT failure or its not wearing the insides of your tyres I wouldn't bother changing.
If you do opt to change them. Do not buy from Ebay. Least not the cheaper ones. They don't line up on the sub frame very well.
This is one of the parts you are better off purchasing the more expensive part.
General consensus here is buy the TRW makes. However I have used Birth from Shop4parts with good results.
TRW cost about £80 for the part. I'd imagine labor will be about £100 a side for a specialist to do it. Dealer I wouldn't even like to think about.
No specialist tools required. Just your usual garage fodder. Possibly a ball joint splitter or two hammers. Which ever method you prefer.
You'll also need a pry bar or crow bar to push the push flat on the sub frame while nipping the bolts but (4 of them) but you must be careful not to cross thread else you'll ruin your new arm.
There are guides on here with lots of photos on methods to do it.
I've done it myself when changing Top and bottom wishbones and drop links. It took me a day to do both in total.
It actually took me two days because the arms I had wouldn't fit the sub frame (These were not cheap ones either)
If you've never done them before give yourself a full day.
The hardest bit is lining the wishbone up and bolting back also splitting the ball joint can be a nightmare. Some just pop no worries. Others you end up spending hours on. My drive side was like that. Two hammers. Two ball join splitters and even a gas gun.
In the engine I just a jack and my dad's weight (Big fella) and hammers to pop it.
You are dealing with rusty bits though. So what can be easy on one car can be a pig on another.
You can re use the 4 bolts. Just make sure you clean the threads.
Alfa 166 2.0 Twinnie - LPG and a few trick performance parts