Back in the early 20th century, Bernard Bosanquet invented the googly, to, in his own words: “ridicule, abuse, contempt, incredulity .” Since then, it's become an almost vital part of leg-spin bowling. I say almost vital, because perhaps the greatest leg-spinner of all time – Shane Warne – rarely bowled one after his shoulder surgery, and still did pretty well. Also, the inverse sometimes applies, the googly isn't a leggie's be all and end all.
Imran Tahir has a pretty good googly. He turns it more than his leg-break, and it's not easy to pick, yet he's just been absolutely smashed by Australia (match figures: 37-1-260-0). He's not s bad leg-spinner, and he has a big weapon in that googly. So maybe he needs to start thinking in the opposite way.
Returning to the early 20th century, Bosanquet started the googly, and taught it to Reggie Schwartz, who emigrated to South Africa. Schwartz became one of a number of googly bowlers in South Africa, which seems extraordinary in today's spin starved country. During the 1905/06 home series against England, they played four googly bowlers in a match several times, in Schwarz, Aubrey Faulkner, Ernie Vogler and Gordon White.
Those googly bowlers helped instigate the first 'golden age' of South African cricket, beating England 4-1 at home, and... Maybe Tahir can take a lessson from them now. All the four were heavy users of the googly, and Schwartz even used it as his stock ball. Your best ball should be your stock ball, no? So why shouldn't Tahir reverse his thinking and use his googly as his stock ball and his leg-break as the change up? He couldn't do much worse could he?