Thats kind of what I did. I have the smallish 4.5" phone which fits in my pocket then an 8" tablet for when I need/want a bigger screen.
We actually have 4 tablets now, one for each family member. When my son kept getting told by a teacher we needed an ipad I gave him the prices of our 4 vs the ipad and so he could see that we could have one tablet for each of the 4 of us or one ipad that we all share and he decided to keep his

Not just maps too, you can use OpenDocumentViewer or AndrOpenOffice for offline editing. I run my own sync server so I'm not dependent on someone elses cloud or even on the internet, since I can sync via my local network.