The series plugin has timeframe functionality which allows download to wait certain time for better quality to appear. There isn't this kind of plugin for movies, but it can be achieved with some clever use of delay plugin.
templates: movies: imdb: min_score: 6.2 min_votes: 5000 seen_movies: strict download: ~/torrents/movies/ tasks: feed-1080p: template: movies priority: 1 rss: http://example.com/feed.rss quality: 1080p feed-720p: template: movies priority: 2 rss: http://example.com/feed.rss quality: 720p delay: 10 hours
This is effectively 10 hour timeframe for 1080p and if the movie is not found by then it will fall back to 720p.
Don't be worried about requesting the same feed twice, it is cached and the second feed does not request it again.