I know this is a year old, but I can give you one of my Guided Tour Systems it can cross sim lines and even teleport past "bad areas" within a sim only - it can, and has gone all over the grid and is very easy to make routes with the global HUD. You can make one point per sim on really long routes, and it stores all the points in script memory to be very low lag and the memory scripts can be copied and added. I have taken 2-1/2 hour tours across mainland. It is a fixed route but as you say, if people made a library or routes from rez points, it would be very fun! - I do sell my scripts at my company though and they are not "open source" if that is a downside. IM me in world would be happy to show it to you and give you one to try!
You can stop by my store (in my profile) to try some of them if you like.