The stock bolts should be replaced when replacing the wishbones.
These replacement M12 bolts are cheaper than the factory items at £1.80 each ref RYG10048 which retail at £3.85 each plus vat. 
A set of 4 will cost you £7.20 plus vat postage and packing .
Picture shows 4 old bolts removed.
These are now high tensile cap headed bolts (stronger than the O.E ones) supplied with square large washers(2) and hardened steel M12 washers.
Also consider the long bolt conversion if changing to poly bushes these require the captive nuts drilling through with a 12mm dia drill , the advantage of this conversion is that does not require the subframe dropping to remove the wishbones as the bolt can be removed from the front.