Do you feel it was indeed an uplifting film, and could you elaborate on that?

Given that it was a fairly violent film, with many (most?) of the main characters dying within a short period of time, I'm unaware of audiences, critics or Japan as a whole tending to think of it as a particularly morale-boosting film, then or now. OTOH I can potentially see a certain uplifting national context from the POV of the villagers, who are rescued from their oppressors by unexpected liberators.

How do you feel a film could boost morale of a country?

From my viewings of Seven Samurai, I think that the most timely or "political" themes of the film was a comparison of the elites and the masses, the powerful and the poor. The character that pretends to be a samurai but is actually from a peasant background, Kikuchiyo, even explains his distaste for peasant lifestyle and culture. While the rest of the samurai debate their role as a samurai and protecting the poor village. The way that I see how the themes of the film would relate to a Japanese person in the 1950's would be related to a government/citizen group works together, and how to maintain a relationship between the powerful, productive, weak, and old.

That being said, the massive success of the movie undoubtedly brought a huge focus on Japanese film and entertainment for decades to follow (we're even discussing it right now), so in that particular sense, it was a huge boon to the Japanese film and entertainment industry.