But I've built a few kits, repaired at least one dismembered wing panel, and made mistakes along the lines you describe. It seems like I'm constantly gluing things before they should be glued and having to improvise fixes.

I would suggest making a doubler for at least part of the rib and gluing it to the inside of the existing rib so that the spar will have something to attach to.

That would be cheap, very little effort, and if you use cap strips will be invisible.

Good luck.