I would say this is really a decision you need to make alone,and should maybe factor in that if you sell the golf and keep the rado and then decide you dont like it as much as the golf after all,will you get another mk2 in the same condition and the same year as yours for sensible money?
As im sure your aware well looked after ones are just going up and up.
As for the engine i think you'd probably get more for the car with the 2ltr 16v engine and get alot more people interested in the car but on the other hand,IF you did decide to get another golf down the line,if you sell the car with the 8v engine then ud have the 2ltr 16v to put in the next golf u bought rather then have to start from scratch again (presuming you would want to convert it to a 2ltr 16v).
Id say its a tuff decision mate.
Good luck.