RCD 310 I believe second gen radio, so you might need upgrade canbus to prevent battery drain on pre 2007 golf
Easy ? Hard ? Costly ? Worth it or NO !!
Not hard, if you know what you doing. Canbus around £70 + codding+ headunit price.
Worth it or No? Yes worth it, sound quality much better than older units, if you can get DAB version -even better.
Do you have MFSW in your car? If you running already aftermarket unit "kenwood" you probably won't notice much difference in sound quality.