Hi Dave,
I can give some insight into the variable star observations and spectra, as I manage those BAA databases.
BAA Variable Star Section Database: http://britastro.org/vssdb/
BAA Spectroscopy Database: http://britastro.org/specdb/
It used to be that amateurs and professionals would request this type of data by contacting the Section Director, and this still sometimes happens. However, it is now far more common for them to simply download the observations from the website. We have notes on the database websites asking researchers to acknowledge the use of the data.
We also send a copy of all our variable star observations to the AAVSO once per quarter. While researchers will often come to the BAA databases, some researchers may only look at the AAVSO website, in which case sharing our observations makes them more widely available and useful. The AAVSO acts as a bit of a central hub for variable star observations, receiving observations from a number of global organisations. The AAVSO acknowledge the individual organisations as well as the observer in the data. It is important to note that the AAVSO database does not store all of the information that is held by the BAA Variable Star Section database. In particular we additionally record the chart and comparison stars, so that light curves can be updated when more reliable comparison star magnitudes become available. Something which has happened many times over the decades, and otherwise causes unreal bumps and dips in the light curves.
The BAA Spectroscopy Database is relatively speaking quite new, though I already see it referred to amongst the spectroscopy community. With time it will become better known, as observers refer to it in their communications, and interested researchers are pointed to it. There has been an example of this in the past month with a Pro/Am project looking for a place to archive historic spectra, so they can be made available to researchers for download.
There are also a good number of dedicated campaigns to observe particular targets. Though I primarily make variable star and spectroscopy observations, I see these going on for solar system targets as well. Those involved in these campaigns will usually have an understanding of how their data is being used.
Best wishes,
Andy