3 questions..
>
> 1 - is there a noticeable difference between the power
> of a 1.9L and a 2.1L?  hills, mileage, etc..?

Have never driven a 1.9L, so I am unable to comment on this.

 2 - what are the advantages/disadvantages of having a
> water-cooled versus air-cooled?
>
Water cooled should be more quiet. Have lower operating temperatures. A real heater to warm your interior, especially useful here in Alaska. Cylinder heads won't rattle themselves loose. Longevity?
Disadvantages of water cooled, $500.00 worth of cooling system hoses not including pipes to front of vehicle. Having to bleed air out of cooling system after fluid changes, repairs, etc.

 3 - why, if the camper westfalias have more 'stuff',
> do the weekenders seem to cost more; what is a 'fair'
> price for a weekender? (i'm in norcal)

I have never seen a Weekender priced more than a Westy, and we purchased our 87 Westy Syncro in Berkeley. As for fair value, the bottom line boils down to a good deal is one in which both the buyer and seller are satisfied with the amount. The only real way to determine fair market value is to take the time and shop as many vehicles as possible before making a purchase. Be sure to have a competent shop inspect the vehicle for condition of engine, transmission, body, etc. It is also important to run a vin check, I believe that somebody in California rolled our odometer back almost 100,000 miles. Our van is in good shape and the engine has 160-170lbs compression, but we would have offered less had we known the true mileage.

Mark
87 Westy Syncro