Tbh, I'm not really sure what advantage having the ISIA stamp has anyway, I did some extra courses on top of my NZ L3 in order to qualify for it and I have yet to see any benefits. I had thought it would make working abroad easier, but in Argentina it's not recognised, despite them being also part of the ISIA.
I don't know how it is now, but 10 & 20 yrs. ago having an ISIA stamp pretty much guaranteed the royal VIP treatment at most areas in the Alps. I remember at Le Grand Montet, as soon as I flashed my ISIA card the liftie whisked me to the front of the line . In many places skiing & some trains were free & if not, cost was greatly reduced. I think it must have been the ISIA card that got me that treatment, because I can't believe it was my charm alone . Other than that, I don't know of any other advantages.
Took it with me to Canada a few years ago, & got a bit of a discount, but it was pretty inconsistent. It seemed like there was no set policy there.
As far as raising the LIII standard, from my POV this would require stripping all current LIII's of their pins. The standard & level of understanding is what it is & always has been. I have seen an odd year once in a decade or so in a given division, where maybe some folks slid through or it was thought to be an easy exam. If you look at pass rates over the history of PSIA, I think you will find that the percentage of success at LIII has remained pretty consistent at around 30-35%. The only way to raise the standard would be to add a LIV... IMO. The requirements for a PSIA LIII, are nowhere near the requirements of the highest level of certification in a country like Austria for instance, where certification may require snow assessment, route finding & crevasse rescue skills.