In my opinion, don't worry about weight, concentrate on aero. I live in hilly country( Vermont) and use the hills to my advantage. With an added passenger( my son who weighs 260 lbs plus), I see little overall difference in mileage, more going uphill, longer coasts going downhill, pretty much a wash.
I know that the MKI and MKII are a bit different, but there are a lot of similarities.
I would suggest an upper grill block, full belly pan, and, if you really want to get wild, put a tail on that wabbit.
If you have the 4 speed, your top gear ratio is the same as my 5 speed with my re-geared 5th. If you have a 5 speed, there are options for re-gearing 5th
here that might benefit you.
Keep (V)Dubbin'!