How to add detail to a mesh without subdividing all of it Kind of a simple/noobish question here.

I have this simple model:



Now I want to add details to it. Like, rounding up the ring, add something to the hilt...
But I'd like to keep the model "light" on the polygon count. But if I add a loop cup on the hilt (for example) lenght-wise, it'll obviously subdivide the blade too (which doesn't really need it) and the ring. 
So what would the best way to add detail whitout adding unnecessary quads where they're not needed be?

I though about dividing the mesh in three pieces like this: 


But this way, after adding what I want, I'd end up with a different number of vertices between the (for example) the ring and the blade, this way I wouldnt be able to reconnect it the right way, I'd end up having to add traingles to the mesh or leaving seams.

I don't think that simply connecting the pieces in object view so that there is no space between them would be the right course of action, right? 
Or maybe it is? Because I remember this human model I downloaded, and it basically had the face, the hair and the body as separate meshes, that were basically put together in object view without leaving visible seams but not connected into a single big mesh.
I recommend to have separate mesh objects. My rule: "What is separated object in reality should be separated object in 3D too", because it simplifies many things: modeling, texture mapping, material setup, animation, etc.