Would you make the same argument for lists of translated resource node names? These used to exist as a library in Babble 2.2, but were intentionally not ported to Babble 3.0. Such code is very straightforward and is unlikely to require much maintenance, aside from updating for new expansions that add new resource nodes. I don't see any problem with copying and pasting this kind of stuff around.
I would. Why make people copy/paste (and spend that time) when instead one centralized place could do the updating and solve the problem for everybody?
Also, say there is a typo/bug. What is the impact of the typo in a lib, and in distributed code that is copy/pasted? How easy is it to fix it and get the fix to everybody?
The answer to both is that it doesn't behave well in terms of easy and time needed to add/fix the situation if the paradigm is copy/paste. It is easy to fix and has non-duplication on time investment if the code is a library, and it propagates gracefully.
I am no fan of copy/pasting as a code-sharing paradigm for sure... I can see cases where it's sensible, but I do have a problem with it in lots of cases.
Copy/paste is a really poor way of doing core sharing. Updates do not propagate.
If there are multiple instances of addons using sharable code - I am pro lib, but I know that powerful people have very specific stances on the whole lib deal. This may be one of those cases where that's regrettable.
Let me shoot into my own foot here. People are very unlikely to run more than one addon that uses LibFail, yet the fact that it exists as a lib is a god-send, but frankly for no other reason that LibShieldLeft would be helpful.
Also LibBossIDs is very unlikely ever going to be used by more than one running addon yet having it this way makes code sharing/propagation between addons viable.
So my vote is clear in this case: It's your call. If it does make your live code sharing easier (either on the maintenance side or the propagation side), make a lib.