I know that a sweeping revision of renoise instruments is on the backlog, but as a stopgap measure something that you guys might consider is a Track effect that exposes the parameters on the Instrument page.
So that instead of looking at other fx in the chain (like the Automation plug), it looks at the parameters that you see on the Instrument page:
And each Renoise Instrument Automator would only let you select one of those above. When you selected one, it would expose the following parameters:
—Envelope amount (this would have to be a new Instrument value I guess, but it would scale the envelope up and down)
—Envelope Length (this would have to be a new Instrument value I guess, but it would scale the envelope left and right)
(except for Filter Type which would just be a straight selection of the Filter Type).
This would be sweet because you would then be able to automate this stuff with pattern fx and lfos.