Now, I am not much of a hiker (being an avid couch potato), but I know that the Mandement, although certainly full of vineyards, is also home to much of Geneva's industry, so the chimneys of the incinerator omniously loom over what would otherwise be a beautiful landscape in Satigny, Russin and Aire-la-Ville. Dardagny itself is very pretty, but La Plaine has little claim to charm.

So I would even go as far as to recommend heading straight to La Cote -- now where exactly I am not sure, but perhaps around Tartegnin, Mont-sur-Rolle and Aubonne (there is an excellent although not cheap restaurant in Aubonne called L'Esplanade and in Bougy-Villars you can get the best chocolate ever from Tristan http://www.chocolatier-tristan.ch/entree/entree.html)

Having said that, if you decide to go to the Dardagny-Satigny area, I think that Café de Peney is definitely worth it. Domaine de Chateauvieux would be too much of a splurge for lunch, but chef Philippe Chevrier is the owner of both, therefore food there is very good. Plus he has his own cellar and I remember that his cabernet franc was quite memorable.