Ti springs are ~$250-300 to save just as many grams. Work it out - do you really want to spend $1 per gram you save? Manufacturers won't spec $300 springs because chances are you'll have to change it anyway.
For those claiming better suspension performance - sorry, all bullshit. The numbers do not back it up at all. "Better memory"? No. Lower unsprung weight? So insignificant it's not worth considering. Better life? hahah - sure, if you put your spring through like 100 billion cycles. Otherwise, no.
If you buy a Ti spring, don't try to kid yourself that there is any benefit whatsoever other than lower weight, cos it's just not true. If you really do want the lower weight then go nuts, but it won't make the suspension work any better no matter how badly you want it to.