each with x/y pos and up to 8 neighboring/reachable nodes
OK but isnt your map more irregular than that with varying edges and chokepoints (portals) to be using that more generic 'network' of nodes ??
Anyway, if as implied in the highlight above you will still have a regular grid pattern overlaid over your tile type terrain so the same algorythm can be used (the distances/costs might be now derived/calculated preprocesed from the tiles).
Wont you still need a 'fine detail' pathfinding/navigation on the tiles themselves for object movement OR you are now navigating/moving only off lines of the course network --and are you sure that wont run into conflicts with some tiles (assume the edge lines are clear)?
A hierarchical pathfinding system can make longer path processing more efficient as long as you map is large enough to make the added complexity worth the trouble.