If you're looking for a list of passenger rights as to what you're entitled, I don't think you'll ever come up with anything. (Like the airlines really would take the initiative to do this!)

Mechanicals are a drag, so are delays...they happen. Sounds like they gave you some compensation and got you to EZE.

Any costs you incurred and did not get to enjoy due to the late arrivel (i.e. add'l hotel night) that you can prove--it may be worthwhile to write to see what UA will do in the spirit of goodwill <> your 15 years of being 1P.