Hi Kate
I had very much the same dilemma when I started my researches a couple of years back - but have finally concentrated on the 4 parental branches of my tree (i.e my parents and my wife's parents).
It is very easy to get dragged onto tangents when you find a plethora of information available to take you in that direction - but there's no harm in looking when you have the time and it's part of the fun isn't it

The real fun starts when you get the same surname cropping up in a number of families but in the same geographical target area - trying to understand the dynamics of those relationships (i.e. how does Bill Blogg's family tie in with Joe Blogg's who lives a few streets away) can be really challenging - but very rewarding when you discover another line of relations you were not aware of.
Thus I would say go where you have the time and where your main interests lie - but don't be too hard on yourself when you find you are drifting from the main focus of your researches - just enjoy yourself
Best wishes for your researches
Dave