Are the upgrade offer emails you receive a couple of days before a flight any good or valuable?
Received this offer email for my flight from Johannesburg. (my full itinerary is JNB to LHR).

Currently via the manage my booking page, I can upgrade the full flight to business special for £983
I personally feel this offer is not worth it, especially if the T&C are as attached (no lounge access, no priority check-in, no priority boarding, no business class miles earnings