You are using rather in a specific sense of the word, which expresses a preference. This sense of the word is signaled by the accompaniment of would:
I would rather eat a hamburger than eat a sandwich.
The sentence you gave is simply a contraction. The words I would contract to I'd, but it's still the same semantically.
I don't think that any sense of the word rather expresses a value judgment, per se. You are right, in that preferences are not necessarily value judgments. They are most often subjective.
Consider,
I would rather have these glasses than those because I am near-sighted.
The other pair of glasses could be perfectly good for far-sighted folk, but since I'm near-sighted, I prefer the glasses that work for me. This is not a value judgment, since the far-sighted woman sitting across from me on the bus, trying very hard to read To Kill a Mockingbird without a pair of glasses, would rather have the other pair of glasses, because they would work better for her.
In summary, I don't think it's the word rather on its own which creates a value judgment, or the appearance of one. I think it's the context which creates the appearance of a value judgment.
Here's an experiment. I'm with her was one of Hillary Clinton's slogans. When Oprah said it, did she express a value judgment? Probably. But do these words on their own create this value judgment? No. It's the context.