I suppose the advantage with having the strut tops cut and adjustable top mounts fitted is that if you choose carefully you can get caster adjustment ones as well.
Short of shimming the TCA arm/ARB junction there isn't an easy way to increase caster on a standardish Cosworth front set-up is there? I've noticed a few recent articles ( esp on the 3-door rwd ) commenting how they don't have much self-centreing action compared to modern sporty cars. The caster also helps preserve the -ve camber on the wheel as you turn it which helps keep the outside wheel flatter to the floor as you roll onto it in a corner