I don't think there is a good reason for not compressing on a utag.link call. We can add support for that. I'll put that on the list for the next SC template update.
For the second request, the "chaining" of compressed values gets a little more complex. The compression algorithm in the Tealium SC template right now doesn't try to more that the basic substitution when entire values match. This is typically all you need to stay under the 2K limit for IE pixels and send maximum data to Adobe data collection servers. That said, we can build this if you need support for a more complex compression algorithm.
Ideally, we'd like for SiteCatalyst to build this logic into their tag by default. Can you reach out to Adobe/Omniture and see if they have plans to build in this algorithm? We'd also like for SiteCatalyst to behave like another analytics tag (Coremetrics) that only sends the browser plugin data on the first hit of a session. If we can just help one tag vendor reduce their pixel size then we've done our job to save the internet.. and the planet.. from unnecessary data transfer. :-)