Thank you for inaugurating this very interesting discussion.

In a way there are three Natsume Sosekis:

1. The writer only known to readers (like me) through translation.

2. The writer known to readers somewhat familiar with the Japanese language (say after 2 years of formal study in a university, or thorough immersion).

3. The writer known to readers fluent in Japanese.

Each writer is a little different--obviously fluent readers can pick up more than the other two groups, but this doesn't mean that other readers can't bring something to the table.

There's another category: texts in a language that's no longer spoken (or perhaps never was, as with Sanskrit). No one today is likely to have the fluency of the original audience. An aside: I took two quarters of Sanskrit in grad school; two of the students in the first quarter were from India, but the class was so heavy with grammatical and linguistic history that the two students (who weren't literature / language majors) struggled with the simple excerpt from the Mahabharata as much as any of the students whose first language was English, and they didn't make it to the second quarter, where we read some Rig Veda hymns--very painstakingly. In cases like these, there's always going to be a distance.