Originally Posted by Alleran
You'll need the Node Spellcasting feat to make use of them, but tapping into ley lines is often serious business (e.g. Birthright), so it makes sense to me that you'd need some investment in the option.
True, but it also means that a character would need to spend a feat slot to access a source of power which he may or may not spend much time around. Unless ley-lines are effectively everywhere, not everyone will see this as a good investment. It depends on the density of ley-lines across the landscape and the benefits they provide.

Originally Posted by unseenmage
I havn't even given any thought to how they'd be implemented rules-wise. ...I've considered that they could be Mythal-like....
I think the mythal approach gives you the opportunity to provide benefits to a broader range of spellcasters. Say each particular ley-line grants a certain benefit to anyone casting within its effective gradient--maybe a +1 CL on electricity spells, or a doubling of the range for Dimension Door if you 'port along the ley-line, or an extra d4 on healing spells, etc. I would see the ley-lines as being extremely narrow, just broad enough for a single person, and not always easy to find--perhaps a Detect Ley-Lines cantrip, so there's a slight investment in finding and casting from one.

Casting at a convergence of ley-lines would provide the benefits of each component strand, but there should also be some emergent effect which can only be tapped right there at the hub--something a little more spectacular. This, in fact, would be a good place for Node Spellcasting or something like it, since it makes sense that those who seek out and specialize in convergences would devote a feat to it.

So maybe a two-tiered approach: a basic benefit from each ley-line, a slight and very specific boost in power to anyone who spends a cantrip and the time to locate a ley-line; and more powerful benefits from casting at a convergence of ley-lines, which would require a feat to access in full.