Very well put.
These kinds of interactions are a way to show off how cultured or educated you are as both the doer and the receiver. Someone in an inferior position (kohai, newbie, younger person) should make an effort to support his/her superiors, or to at least make the lives of their superiors more pleasant by doing things like pouring drinks, clearing the table, arranging the shoes in the genkan, etc... So the kōhai should pour for the senpai.
Enter the foreigner, and the equation becomes slightly more complicated. If the foreigner is a guest, or is new to Japan, the senpai/kōhai hierarchy becomes unclear, and the Japanese hosts may default to a status where they treat you as a guest and pour drinks for you (and don't expect you to do anything in return because you don't easily fit into the structure - or you aren't even aware there is a structure). So for the host, it is a chance to show how cultured he/she is to the others in the room by treating you as a guest. Or, if the atmosphere is more casual, the host may just genuinely want to do a kindness for you regardless of the social structure.
In either case, it is natural for you to accept this kindness humbly and (as mdchachi puts it) somewhat reluctantly, with mild protest at being on the receiving end of such undeserved kindness. Mild is the key word here, as I find it embarrassing when people get into politeness duels, loudly and dramatically refusing these small gestures. One sees this on the train: a group of middle-aged people will energetically argue about who should take the empty seat, each trying to outdo the other in politeness. It ends up being annoying for everyone. Anyway, if the offer has been made to pour for you, regardless of the hierarchy, it is only fair and polite to at some point reciprocate the kindness, and offer to pour for your host/superior and others around you. This allows you to show that you are also cultured, and that you want to repay the kindness. It also gives a chance for your friends to receive the kindness, restoring harmony to the situation.
Dating becomes more complicated because you both (presumably) want to be on your best behavior. In this situation I absolutely would not go on a date with any expectation that a kindness would be done for me. It is the opposite - it is your chance to perform kindnesses for your date. In other words, pour the drink for the lady. It can become confusing because Japanese ladies may go into the date with different expectations. For example, a Japanese lady may not expect to have doors opened for her (well, to be more clear, Japanese ladies may be taught that it is polite for them to go through the door lastly). So it can be awkward if you hold a door open expecting a lady to walk through, and she doesn't quite know what to do since for her it is polite to go last. I still face this situation with my wife after (cough) decades of living with her. For me its natural to hold elevator doors open for her, and for her its natural to let me be the first to exit the elevator. At any rate, the attitude should be, "let me do this kindness for you". In Lomaster's date situation, where the lady poured for him first, then poured for herself, it was an opportunity for you to jump in and say, "let me pour for you" (thereby returning the kindness). If the whole thing was too quick, then look for the next available opportunity to pour for her.