i don't know about detailing experts' takes on this, but based on personal experience, plastics when discolored remain discolored. you can only do so much to ligthen up the discoloration but will remain that way.
i only use two things to maintain my interiors, armor-all multi purpose cleaner then armor-all protectant gel. they're not expensive and do a very good job for my two cars. spray on the surface of your shift knob and handbrake and let it sit for 2-3 mins then wipe with clean cloth. i'd apply some gel as well to give it a new clean look.
or, if you don't mind spending 3,000, just take it to the professionals. take it to bigberts for a full interior detail and give your Innova's interior that new car feeling.
or, just buy yourself MOMOs...
