[Formendacil]

It's also worth noting that although Beren gets a fairly impressive lineage in the Silmarillion, as well as a fairly heroic backstory in his pre-Doriath exploits, these parts of the tale were not part of the original Tale of Tinúviel, but came with the development in the Silmarillion post-Lost Tales.

In any case, in both the original Lost Tale and in the final form as we have it approximated in the Silmarillion, the key thing to note about Beren is that, in contrast to Lúthien, he does not compare. This is, in fact, more strongly emphasised in the later versions of the tale, where Lúthien's greatness is increased as Thingol and Melian's realm of Doriath and personal power and wisdom are increased--and as the frequency of the Ainur having children decreases. Beren may be the Heir of Bëor and one of Barahir's heroic, desperate band... but as Thingol points out to him, he is a mere mortal, and is not Lúthien's peer in any way save love.

Tolkien also emphasises that it is only because of love and some gift of Fate that Beren wins Lúthien's hand. This has already been noted with regard to how little Beren actually does in winning the Silmaril--mostly just getting into scrapes that need rescuing. Even where Fate sets him clearly apart, such as by finding his way through the Girdle of Melian, this is not because of any merit on his part, but because some higher power gave him a magnificent fortune he did not deserve.

As far as that goes, I think it's easy then to see how Tolkien saw himself in Beren's shoes. The love they won was one they did not really deserve (as Tolkien saw it), one that was only made possible through unmerited love and fate.

Of course, it is ridiculous to try and find biographical points of similarity between Tolkien and Beren, anymore than between Edith and Lúthien--or, for that matter, between WWII and the War of the Ring. It's looking for allegory where one should be recognising inspiration. Tolkien felt himself the luckiest man in the world to win the woman he loved against odds that said he should not--and one may assume Beren felt the same. Certainly, this inspired the Tale of Tinúviel, but that does not mean that an inspired tale will share the details of what inspired it--inspiration means that it is the spirit of something that is taken from the original, not the externals.