I think IMO it would be a worthwhile project, not just for the speedo gear, but there are many old bits of equipment out there [especially in the Audio world ie; tape machines etc] that have disintegrating plastic gears that are getting very hard to find replacements for these days, [I know from experience of repairing this old kit] and who knows' the OP might want to turn his attention to such things once he's gotten the hang of it.
Just a thought.
Ant.