I also have ADHD 
Some thoughts in no particular order, and not necessarily only for org-roam:
If you spend a lot of time writing, Evil (Vim keybindings) is a great way to create little dopamine spikes when you learn to do something more efficiently.
Not specific to org-roam, but adding [/] or [%] to a heading that has tasks inside of it will show how many remains or how many percent remains, respectively.
Doom Emacs + (org +pretty) and also setting checkboxes with prettify-symbols-alist make for very aesthetically pleasing notes.
Organizing notes and thoughts into a hierarchy can be very satisfying. Came across it when evaluating Dendron, and was happy to see that there’s an effort to bring the hierarchical structure to org-roam: GitHub - vicrdguez/dendroam: Bring Dendron features to Emacs org-roam
If you use pomodoros, you can set a sound file to play at start/end/break end, which can be pretty fun. Mine are old Arnold quotes 
And finally, Emacs itself is less of an editor and more of an “elisp evaluation machine”, so the possibilities of tinkering and configuring are endless. This is both a blessing and a curse. If you can stop yourself from falling too deep into rabbit holes, it can be a sustainable source of “ooh that’s a neat thing I could improve” for life.
As such, you can modify org-roam or any other part of Emacs to give you the dopamine hits. A few ideas off the top of my head:
- Count each completed todo and assign a score. Set a daily score goal. Play an audio file each time you complete a todo. Trigger some kind of animation or open a link to your favorite celebratory video when you’ve completed all your goals. (Could also work for org habits)
- Make a shortcut to embed a random gif anywhere you are in an org-file.
- Build a website out of your notes, with an hourglass/timer slowly running out and it is only refilled when you publish a new site (i.e. a new org-roam note).
- Make Emacs start your coffee maker when you’ve completed enough todos / after X pomodoros / X minutes before a timer ends.
Have fun and enjoy the endless dopamine hits of Emacs 
EDIT: Let me know if you end up building any of those things! I’d love to try them out 