As a CSL on WW I struggle with all this. Greeting Gold and Emerald from other OW Carriers is something I try and do (and is now officially my responsibility in the cabins that In work in). It is really hard to personally greet every single Gold/Emerald on some flights. Certain routes (or days of the week, or times of year) we can have many on a flight. Yes even a Miami in July you will find an incredible amount of Golds in WT usually redeeming Avios. I find when i speak to them some love it, some hate it (and make that clear by their reaction) and some are just embarrassed.
I did a trip recently where on an A380 I had 42 Golds in economy on two decks on a night flight. I rushed around trying to catch people before they went to sleep and managed to say a quick hello to about 10. Sometimes it is just impossible.
If I have one or two I will happily offer a bottle of crew water to them (though there is really nothing spare I can offer, and certainly not enough for more than a couple of people). I used to offer a newspaper but these days nobody seems to want them so I have given up as it all takes time and I am usually rushing around and have to operate a trolley as main crew on most aircraft these days.
I do list Golds by area and pass them to the crew member that will serve them and ask for them to say hello and address by name. I think this is well received and less embarrassing for the customer than being singled out with an awkward conversation.