To answer the OP’s question. All Graded/Group races are not created equal. Their "Grade/Group status is relative to the over all “quality” horses running in the country.
A Grade 1 in PR would most likely be viewed by breeders’ in this country as a decent Allowance race. So IMO and most breeders being half to a Graded Stakes winner in PR adds little value as far as a broodmare prospect. A Grade 1 winner would bring a bit more to the table.
But it really comes down to the over all quality of the mares family, pedigree. I am not sure if a P-R “Graded status” is given/used on a sales catalog page. It may just state the name of the Stake and the horse is given black type? Somebody else can fact check.
But there have been some really good P-R Graded stakes winners that are sent to this country and have done very well. So if the half brother keeps going up the ladder he may be sent here. Then the OP has something to get excited about.
Even if he doesn’t but wins a bunch of Graded stakes the OP’s mare maybe have a much higher value as a broodmare in PR. Not lifestyle changing value but more than she is worth as a broodmare in this country. Look up, find a P-R Bloodstock agent and send them an email. Or look up some P-R breeders and do the same. If the owner of the half brother is also the breeder might be worth contacting them. If that is the direction the OP might want to go in.