I've got no experience of the product or scientific basis, but personally I would initially just do the affected area, in an attempt to restore it to a closer match with the rest of the car.
But be careful as the cloudy area may be because T cut rubbed through to a lower coat of paint, which although similar might have a slightly difference colour, paint hardness etc . For instance, it may be clear lacquer in some parts, but through to the basecoat colour in others. The clear lacquer coat is quite thick and can take a fair amount of polishing out, while the basecoat colour layer is quite thin and may rub through to a primer layer quite quickly, even when using a less abrasive polish such as SRP
I would do a cautious test on just a small part of the affected area to see if It is actually improving things. If not stop immediately before its too late.
Also be aware you might improve the affected area, but by doing the whole car the rest might also improve by the same amount and there is still a difference that shows.
A good compromise may be to do the affected area, then leave it to weather , and maybe do the whole car next spring.