Recently, a collaboration of a few professional and very talented amateurs used the 1-meter telescope at Pic du Midi to produce some truly breathtaking images of Venus and the outer planets.
Background information and images at:
https://www.cloudynights.com/topic/580395-p...netary-mission/
and
http://www.europlanet-eu.org/pic-net-groun...-press-release/
One example of the way this sort of data can be utilized is the "Voyager 3" project from Sweden, which used imagery from modest telescopes to monitor Jupiter over a sustained period of time.
http://www.planetary.org/multimedia/space-...-3-project.html
I'd say this impacts on the topic of spaceflight to the extent that it defines the quality of imagery that can be collected on a regular basis with a telescope that is very good / large but not in the top category of size… an important distinction because the largest telescopes naturally have intense competition for their time and are used only for limited numbers of planetary images. It's conceivable that telescopes in the 1-meter class could be used to produce relatively continuous and ongoing monitoring of the planets so far as orbital positions allow. Obviously, spacecraft can always produce imagery of a significantly higher quality, but these earthbound telescopes are beginning to show the ability to approach the scientific potential of spacecraft data sets such as Cassini's imagery of Jupiter or Pioneer Venus' imagery of Venus.