I don't see any immediate compelling reason to update right now, but some thoughts of things that may nudge you to eventually :
- even behind a fireqay, if you have any outbound connections from miniserver to public internet (or even other local devices) it is theoretically a point of vulnerability to potential security exploits
- if you use mobile app then eventually you'll have to update those to a point it no longer works with v13
- eventually your miniserver will die, and unless you have a stock of spare gen1 then it may force your hand in upgrading
- the UI is (broadly) improved in new versions, in particular the energy flow monitor which may be relevant to your self generation plans. Also the energy spot price optimiser. (Otoh the "Energy Manager" is still as primative as it was in v13 and not worth the effort to use IME)
- inverters are most often best integrated via modbusTCP which works fine on older versions and you can probably even import modern Loxone Library templates for them fine.
- the bigger advances in network device integration generally all need a gen2 server too, as they use https and more compute. They also are often cloud-service centric (pretty much all home appliance integrations, and cloud services for heat pumps and inverters) and from your description i think you either want be interested in those or prefer a robust local -only integration anyway
Hope that's helpful. Either way I'd be making absolute sure i have backup of the v13 config installer (in case of PC dying) and it's fairly easy to experiment on a spare SD card if you did want a look
Cheers