Warning, this is coming from fuzzy recollection and some speculation.

I'm pretty sure the Sagres was made from Valite tubing. My understanding is that Valite was rebranded Ishawata Mangy X tubing, but I could be mistaken on that. Regardless, Valite and Mangy X were both used in the first machine brazed frames. This allowed Fuji, Trek and others to bring in lugged frames at a fraction of the cost of hand brazed CrMo frames.

"Value" is quirky thing. If you like the way the frame looks and the way it rides, enjoy it. I have a similar type Trek and use it for my errand bike. Very servicable.