That's more a question about how you use the files as the file format itself. None of those files are merged by default, they keep their layers, so if a layer contains a single symbol (or multiple symbols but spaced out from each other), it is easily extractable from the file, but if the layer contains multiple overlapping symbols, then they aren't isolatable anymore.

Of course, if you merge all layers/flatten the file, then it isn't an issue, but that isn't commonly down with the file in those format, you only provide a flattened export when exporting to a common image format.

Due to the way fill styles are defined on a per map basis in CC3+, old maps won't automatically have new fill styles.

Use Draw -> Insert file, and pick a new map that does contain the style. Now, with the map to insert on your cursor, simply hit Esc, and the fills will be inserted, but not the map itself.

You can still use html if you switch to the Wysiwyg editor. If not, you'll just have to put the hi-res link below the image instead.

My advice, learn and understand the techniques described in both, and use what's appropriate for any given situation. I've also got a blog article here, but it basically uses mostly the same techniques from the Tome.

It could very well be that queue causing issues. Technically, a the dropbox folder is no different from any other local folder, but the dropbox software continuously monitors that folder to be able to synv changes. And whenever it needs to sync changes, it will need to lock the files (it cannot let a file get overwritten while int he process of syncing it, that would corrupt the sync). So when you don't have a queue, the sync is always completed between saves, but with lots of things to do, dropbox may keep the lock on the file for a longer time.