I've got them to 1 teaspoon per 4 litres (1 gallon approximately) and will likely keep on with it until the final week. I think it depends on your personal tastes as to whether or not to feed it right til the end. My guy, who is the smoker, doesn't have a sweet tooth (or is that a sweet lung) so I'll go plain water for the last week.
I'm in the same position as you with not having anything to compare between those who have had molasses and those not, but since the girls seem to take it all in their stride I'm happy to go along with the positive recommendations of others. And its so cheap eh?!