Seeing as how the TCP/IP data source is character oriented, it might make sense to be able to specify a character to be interpreted as end of stream. (like maybe EOT (\004) or something).

I agree, I think that's maybe what was in the author of the help document's mind, but doesn't seem to be implemented as such. In fact, I think the delimiter is currently only used to append to all query or set commands.

One other related question: Is it possible to make the polling rate faster than once per second? For my application, a faster poll would be better.

Yes! If you have updated to the 3.6 beta this would be possible through the new data sources UI, but is possible in previous versions by going through the import / export tools and changing SECONDS to MILLISECONDS