I use my (sadly limited in space) iPhone for Geocaching as well as another program for offline mapping incase I get lost and can't get data service (which here in NE Iowa is everywhere), which results in duplication of map data on my iPhone. Since the Groundspeak application already does offline mapping, it would be nice to have a button that takes me to just seeing the map, which data is pulled from the internet when possible and cache when not. Along with this being able to download instead of small areas caches are like is done now to also say I am going to be in NE Iowa, download some of the zoomed out, less detail maps for this map as well as having some extra data in the app ready to help with mapping of geocashes when offline.
A traveling dash would be nice too, reporting stuff like speed, direction, ETA to a given point, etc, as well as being able to say "oh hey there is a geocache you are about to go past in 2 minutes". I could see this becoming a new feature of every so often (if turned on) the app sends a push notification saying hey you are 1000ft from a cache.