"would wider rear wheels help with the oversteer due to the greater grip?"
Even more important than wider wheels, with these cars it's important to fit and maintain good performance tyres.
 
"Also, in relation to all the negative aspects of Gen 1, such as snap oversteer etc, can these problems be remedied at all?"
You can modify the early model suspension to make the car less lively at the rear.
However, as has already been mentioned it's important to learn how to drive a rear engined car properly, that's the best remedy for snap oversteer IMO.
 

Thanks for the feedback guys. 
 
I've done more reading online about Gen 1 VS subsequent generations arguments and yes, I guess the main thing is to respect the limits of the car and all should be fine. A little (controllable) amount of tail out is a heap of fun anyway.
 
A good set of performance tyres is the first thing I'll get should I get this car. Cheers for the heads up redtarga.
 
Chase-d, thanks for the comments.
 
I'll let everyone know if I do end up inspection/buying.
 
Cheers!
 
Sean