I think you may have answered your own question:
Now its always been my opinion that a
database should only be used if it
speeds things up, or provides a more
reliable interface to the data.
A database by definition provides a more reliable interface to structured data — providing named columns and guaranteed data typing, to start.
If your needs are truly simple (a small number of absolutely consistent fields with no normalization issues) you probably won't suffer too much from using a text file. But how do you plan to analyze the file? Presumably the first step will be to read it into a database or some in-memory data structure. Using a database to begin with means that step is already done for you.
