Oh Ruud that attic clearing is me all over, my son says I am a hoarder lol.
I send my gift balloons in rotation. So everyone gets one every ten days.
I have three friends that are taking a break from the game but will be back, so I use those spaces to send to helpers that are not friends. When they all return it will have to be every 11 days.
By doing this rotation I can keep an eye on those that are playing or not, if I find someone is not playing I watch them for about a month or so. If nothing is happening in their town I will remove them.
If the player wishes to re friend me that shows they are around, I will accept them back.
Like you I would hate to hurt someone’s feelings, I believe you should treat others as you would want them to treat you. But hopefully my method prevents that.