I think the main difference is that someone who comes in and fills up their dragon with cheap dragons, as you said, might not stick around, which means those dragons will quickly 'starve' and thus stop having hunger ticks.
However, that person who has been here 5 years, completely maxed their lair, and will buy more lair slots as soon as they are available, are going to stick around, which means that their lair of 210+ dragons are all, usually, having hunger ticks, being fed, then having hunger ticks again.
Which is why I think they do focus on people with maxed lairs, because they are likely to stick around and be 'part of the problem' (not a real problem) with server load. Because it isn't just five extra spaces, it is the OTHER dragons they already have and all the other spaces they can already fill up with dragons, and adding an extra five spaces just adds to that issue.
As for the hunger ticks at rollover, I am not sure how well that would work, but I do know that they did once (at least I have heard this) all dragons ticking down at the same time, but it got too much for the servers, so it could be that even doing a solid 'three ticks down' at rollover might be too much for the server to handle.
Re: Lair/Den size increases
However, that person who has been here 5 years, completely maxed their lair, and will buy more lair slots as soon as they are available, are going to stick around, which means that their lair of 210+ dragons are all, usually, having hunger ticks, being fed, then having hunger ticks again.
Which is why I think they do focus on people with maxed lairs, because they are likely to stick around and be 'part of the problem' (not a real problem) with server load. Because it isn't just five extra spaces, it is the OTHER dragons they already have and all the other spaces they can already fill up with dragons, and adding an extra five spaces just adds to that issue.
As for the hunger ticks at rollover, I am not sure how well that would work, but I do know that they did once (at least I have heard this) all dragons ticking down at the same time, but it got too much for the servers, so it could be that even doing a solid 'three ticks down' at rollover might be too much for the server to handle.