Re: Repair of Teak Toe Rail
I have done this type of repair, although on a smaller scale. Epoxy will be more durable than wood filler, toe rails get a lot of abuse. Adding wood flour will give it more substance, and make it much easyer to work with. The slight cracks will have to be enlarged to get filled, large areas to be built up will need a form built to retain the epoxy (wood strips or stiff cardboard covered in plastic wrap will work).
As noted above epoxy is not UV stable so varnish or paint will be needed. The filled areas will have no grain, so even if you can match the color varnish will have an irregular look.
I have used MAS and System 3 epoxy with good results.
Another option is to replace it. You mentioned that is not your plan, but salvaging metal toe rails from another ruined boat might be pretty low cost. Labor wise it might be a break even proposition as you are looking at a lot of prep work, epoxy sanding and then finishing the rails.