Hi,
A route is usually a lower resolution (much fewer points), and has waypoints associated with each "route point." A track log is higher resolution and has no waypoints.
You don't need any GPS data to download images. You can just zoom/pan to any area you want. Or you can use "Goto Coordinate." to get anywhere. It's much easier to have GPS data for places you're interested -- then you can get there faster.
No the maps won't increase in clarity if you register, unless you count the removal of the "Demo" tiles. However, 2M resolution Topos are turned off by default. They are GIF and slightly slower/redundant, but they are more clear than the 4M topos.
Turn them on in Options->Prefs->Tilesets
Last, no we don't have UTM grid lines yet.