[werk_ag]

...you will soon have a machine which could be applied at many different levels, and at all sorts of costs.

This is the main intention! A weather station that can be built according to the needs and budget of each one.
A secondary intention, is create a system that can be used for other purposes than just observation of meteorological conditions, as agriculture (in general, or in specific cultures).

Whilst I don't want to build up competition on ebay there are some very serious sensors come up for sale occasionally

Which is the case of the one you bought, the NRG-40C. A great quality sensor, unfortunately it's output it's low level AC sine wave, that cannot be read directly by the WeatherDuino Pro2 TX unit.
Anyway, I think that with the help of a simple Schmitt trigger circuit, to convert the sine wave frquency to a pulse with the same frequency, the NRG-40C could eventually be used with the WeatherDuino Pro2 system.

While I think about it can you make the potentiometer reading flexible ie Davis is 20Kohm, http://www.qsl.net/on7eq/projects/arduino_davis.htm . I have the Didcot wind vane which has a 1Kohm super low friction potentiometer fitted.

Do you have specs of the Didcot wind vane?