Many templates? I can't think of many templates that won't contain the user data if that template explicitly deals with user content.
There's a few things to note here; queries which only select a subset of the data from a table are going to be few and far between now, as the new Finder system will usually return an Entity object which represents the entire data from that table, and any Relations (joins) as well will be available automatically if specified while constructing the query, or even available on demand.
For example:
PHP:
$finder = $this->em()->finder('XF:Post')
->where('thread_id', 123)
->with('Thread')
->onPage(2)
->orderByDate();
$post = $finder->fetchOne();
$thread = $post->Thread; // this was fetched with the query
$forum = $thread->Forum; // this is silently fetched as needed
if ($forum->canView()) { /* ... */ }
if ($forum->isUnread()) { /* ... */ }
In this example we are fetching posts "with" their related Thread data (this means the resulting query will do a left join) but we can actually call "Forum" as well, which is silently fetched (at the cost of another query).
This means, in this scenario, even though we haven't explicitly called the User relation (to fetch the user records of the post authors) we can still use "->User" on demand to fetch that. Of course not ideal if you're dealing with a massive amount of posts, but there is some caching involved there.
Even so, I'm not sure you realise how avatars and the avatar_date work.
The avatar_date field is used for two things; a) an indicator that the user has a custom avatar and b) a cache buster. We do not store multiple versions of a user's avatar. We only store the latest.
This means you can always rely on the fact that if they have an avatar_date field, the latest version of their avatar will be in data/avatars/(size)/(x / 1000)/x.jpg where X is merely their user ID. If someone uploads a new avatar, the avatar is stored in the same location as the previous one. The avatar_date is useful there because if we know when the avatar changed, we can append that to the URL of the avatar and that will invalidate any browser caches and ensure that everyone sees the updated avatar instead of the old one.