Thanks for the great question!
There’s no purpose-built method of doing this that is baked into our plugins, but your thought on using a ticketing plugin is an interesting one and could definitely work (though you might need to make a few tweaks to make it feel ‘natural’).
It looks like you already have Event Tickets Plus and so I guess you’ve installed Event Tickets itself, which offers free/RSVP tickets — perhaps you could indeed use RSVPs and do a bit of relabelling to present them as a “Things I wish to attend” button.
With some relatively low effort custom dev, you could also build out a per-user list of those events they have “RSVP’d” to. Getting into the nuts and bolts of such a change is a little beyond the scope of support we offer here, but please do feel free to ask if you have any specific follow-up questions and if I’m able to answer or just point you in the right direction I’ll be happy to do so 🙂