That's why the "easy way to reopen" is so important. Your concern is theoretically valid, but if tickets are usually ignored for years, then it really is a desperate situation for the project whichever way you handle it. You can decide between an endlessly growing list of issues that likely aren't valid anymore, or pissing some users off.

I don't really see why it would be harder to find an existing or similar bug. You should be looking (or rather you should be automatically notified) before/during creating a new ticket for existing tickets describing the problem. If a closed ticket describes the exact problem, you should be finding that too, and then should just be able to use the easy way of reopening if necessary. You should also be able to find the workaround in there if someone posted it.

It's definitely not a beautiful solution, but if you implement something like this, the project is already in a desperate state, there's not too much good choices there anymore.

I... know... that's why I explicitly mentioned this already xD

Well the reason to auto-close is that this is not an entirely unlikely resolution. When I inherited a project with a bunch of issues and started going through the backlog, around 50% of tickets were duplicates, already solved, unreproducible, etc etc

When you've only got limited time, having less of those issues to analyze and then close anyway is a very valid reason. It leaves more time for fixing real issues. Of course it comes at the cost of ignoring perfectly valid issues as well, that's why this is obviously never an optimal policy to implement, and should only be done in desperate situations.

The close message should just say exactly this. If it's one click to reopen, then the click is the response to your suggested notification.