tbh, on other bikes where parts might cost significantly more, then yes id recommend a topset overhaul to prevent further damage. In FZ's case, id just use it till the engine breaks down, then have it rebuilt, as the parts are cheap and plentiful, heck you can just spec it up just for fun without it costing too much money as aftermarket components can be found in almost all ali, ah seng and muthu shops.

10 years bike, consuming 1/3 of oil engine oil, that's not something a VC or filter replacement could fix. Unless you can get a real good bargain for a topset overhaul, id just ride it till it breaks. You prolly have a leaky valve seal or a worn piston ring, whichever the case, you'd have to open up block/head to fix.


As for other things you can do make it ride better before the need for an overhaul (assuming you keep basic maintenance in check)

You mentioned engine stalling and unstable idle, this is probably dirty throttle body, ISC, or fuel/air related, could also be bad ignition coils. Worst case could be due to low compression, a shop that knows that they're doing can run a quick compression test, and will take less than 5 mins, doing a compression test eliminate engine factor in troubleshooting.