Remember that insurance groups mainly refelect the situation when a car is new and take into account things like parts prices/likely depreciation as a very large component.
The RSi is an informed choice, but hardly worth it over a 16V. Remember that the 16V was also the homologation car for Renaultsports Group A/N WRC campaign (before the Williams) and comes with a lot more than simply 27bhp and a higher insurance tag than the RSi. Theres obviously the engine, cooled and moulded over by that bonnet bulge; much wider tracks and totally revised suspension, covered by the fat arches and bigger bumpers; and then theres also the seats, dash and eveything else that makes them damn sexy.
You can debate the 0-60 all you like, but its a crude measure and remember that a Williams is only fractionally quicker than a 16V to 60 anyway. 7.7 (16V) plays 8.9 (RSi) - but then an RT is about 10 secs...maybe we should all get one of them instead! Despite what people say, the Valver is also a torqey motor - it gets a peak at 2-3000rpm, but stays flat until 5000rpm when all the fireworks start.