Is it worth upgrading from non-cup to cup? not really.
Buying a cup over a non-cup, possibly. But you will need to be Mansell to notice any difference.
Given we're talking about cars that are nigh on 10 years old now, the condition they're kept in will dictate how they ride more than what parts they came out of the factory with.
Indeed, as you'll see on CS, many of the cars will have had the well-sorted Renault set-up replaced with "developed overnight" coilovers for epic lowz etc. Under the impression that low=grippier.
Which is not necessarily the case.
Summary - Stick with what you;ve got, get geometry done, maybe review what rubber you're running and refresh the now creaky or rusty bits.