Carlos - one of the main areas that the Willy is different from the 16v is the suspension, but its not that much. Basically the Willy has a 34mm wider front track (created by using different offset wheels), lower wishbones from the 19 16v, different shocks all round and different front springs.
The mods obviously have the desired effect in that the Willy is still regarded as the best hot hatch ever by many people, but theres nowt you cant do to a 16v with minor expense! The 16v obviously still uses the same shell, has the same shock mounts, rear torsion bars and weight balance. Theres much, much more of a difference between the Valver and the 1.8 RSi than there is between the 16v and the Willy.
Id say that if you have driven a Willy, then you know what to expect from a 16v.