A Cat 3B ILS would certainly be a major improvement at Perth, but it only solves part of the problem. The other problem is the lack of a decent alternate within a reasonable distance from Perth.
Although LVO would allow most jet aircraft to land and facilitate fewer diversions, the airlines would still be required to carry fuel for an alternate. As things stand, the nearest alternates some international carriers can plan are Adelaide or Bali. That means a lot of extra fuel has to be carried by the time we take alternate and ETOPS fuel considerations into account. If we have to plan Adelaide as our alternate, with Darwin and Adelaide as the ETOPS alternates, then we will land in Perth with around 25 tonnes of fuel (A330). That seriously reduces the revenue payload we can carry and it also costs a heck of a lot just to carry the extra fuel.
The best solution would be to upgrade Kalgoorlie or Learmonth with decent parking facilities and RFF, but I doubt anyone wants to pay.