"Worth it" is of course going to be a different decision process for each owner. I try to buy the service manual for any vehicle I own. Ideally I end up with a print version for reference at home, and a digital version for on the road, though either or both options are not always available. That's just my personal preference. I'm someone who reads and writes technical documentation and one of my bikes is plated "RTFM" to reflect that.
Many of the model year differences are called out in
https://hondatrail125.com/index.php...-downloads-owners-service-parts-catalog.1189/
Some of the notable changes in terms of regular maintenance for the JA65 are the addition of a disposable oil filter that needs changing, different oil change capacity depending on filter vs no filter change (noted in the owner's manual), a different spark plug (noted in the owner's manual), and different valve clearances (noted on the swingarm sticker). If you are replacing parts and need to know what gasket to order, a freely available online parts fiche/catalog will be your source for that information rather than the service manual, so IMO the JA55 service manual probably carries over well to cover the basics of the JA65 and any other information you need is likely already on this forum or someone would be willing to provide it if you really wanted to get by without the service manual. There are even YouTube videos that will walk you through many of the maintenance items.
Personally, if I added a JA65 to my fleet, I'd drop the $$ on the service manual specific to it even with knowing it's not much different from the JA55 one. The service manual + common manual + owner's manual end up being very comprehensive, and if you have the correct manual for your specific model then the information is more easily available and you can use it as a source of truth rather than needing to validate something you found online. As much as I think Helm's shipping cost is ridiculous when they could probably be using very inexpensive USPS media mail, I support right to repair and "vote with my dollar" that I want Honda and their bookstore partner to continue to make manuals available for purchase by the general public. Everything I've bought from Helm Inc has shipped FedEx.