If there is no play in the offside bushes I would not replace it. New arms are a bit of a lottery. Some last for years some only last for a few months! Even OEM ones can be poor.
There is almost no danger of a catastrophic failure and having a slightly worn one on one side will not have any effect on the wear rate of the new one.
I always make sure that I give the bushes a good spray with good quality silicon lubricant before fitting and top up if there is ever any sign of a squeak. My own theory is that if the bushes are squeaking badly they are generating heat and the poor quality rubber breaks down. Could be wrong but the bushes are generally rubbish quality.
I would get the alignment done after fitting though as tyres are expensive these days!
"When you sit in a Focus RS or a Golf R32 itís like sitting in a commercial for Lynx aftershave. When you sit in an 147 GTA itís like sitting in a Venetianís hand-made suitcase." J.Clarkson 2003.
Current fleet: 156 Sportwagon jtd 16V (facelift) 2.4 Spider, Leon Cupra SC
Projects: Spider S4, Matra Murena 2.2