I do care about upgrades and I am always happy to get one.
So I ususally write an email beforehand mentioning that I would appreciate an upgrade very much. Sometimes there is no reaction, sometimes no answer but a pre-assigned upgrade, more often than not I get a nice answer and some upgrade - either pre-assigned or at check-in. The upgrades differ, rarely a suite, sometimes junior suites, usually executive floor rooms (which I consider 'fake' upgrades if this does not involve a larger room or view with room since DIA have access to the executive lounge anyway).
Where I am a returning guest I started getting frquent upgrades. Also when staying on points. However, this applies to Europe, not the US.