On the client side, Discourse does not serve any javascript assets for disabled plugins, so there won’t be any impact there.
On the server side, for properly implemented plugins (which all of these are), customizations from plugins are bypassed when they’re disabled. So yes technically there might be a slight overhead to check for enabled/disabled state, but it should be miniscule.
The plugins we’re merging here are the ones which we run on every single instance of Discourse on our discourse.org hosting. So they’re all very well-tested at scale.