I adjusted the user rights of my wiki so that any user could view "Special:DataDump" and so (auto)confirmed users can delete old dumps and generate new ones. In theory, this would allow disgruntled community members to fork the wiki without asking me (or whoever caused the hypothetical disgruntlement) to generate up-to-date dumps for them. I limited the deletion and generation of new dumps to (auto)confirmed users, since the absence of a "Special:Log/datadump" page means that vandals could vandalize the wiki or post dox and then stealthily replace a good dump with a vandalized or a privacy-compromising dump if such a limit on privileges weren't in place.
Anyway, by allowing a wide group of users ((auto)confirmed and above) delete and generate dumps, it would become difficult to know the precise age of a dump. This wouldn't necessarily be a problem for users that possess all three relevant rights ("view-dump", "delete-dump", and "generate-dump"), since such users could just generate a new dump without concerning themselves too much about the precise age of the old dump.
A problem arises, however, when a group has the "view-dump" right but not the "delete-dump" and "generate-dump" rights, and that is the situation I have on my wiki: everyone has the "view-dump" right but only (auto)confirmed users have the "delete-dump" and "generate-dump" rights, which means that non-confirmed users would be downloading a dump without knowing how old it is beforehand.
Thus, I believe that it would be beneficial for "Special:DataDump/view/xml" to display timestamps next to the file link.