I am pretty sure they don't limit Grab Wallet to Malaysians only (at least when I signed up for it). If I recall correctly, it was just there. What users here experienced is they can't topup their wallet using a foreign Visa CC but they are able to do so via a foreign Amex/Mastercard CC. I tend not to use any of these wallets as this means the cash portion is stuck in there and I have a feeling it will be a pain to withdraw them.

You could certainly top up the wallet with a Singapore Visa card for rides until late last year. I've never tried to use the wallet for anything other than rides though.

What is the benefit of topping up a wallet as opposed to Pay per Ride?

Perhaps, the foreigners excluded were the nationalities that don't have Grab in their home countries. I remember one pop-up when I opened Grab in a new country asking for my nationality and then just closing the screen when I selected United States. I assumed it was a question related to the wallet functionality.

You earn more Grab points pesos. They are pretty much useless anyway. But topping up with a wallet means you can pay brick and mortar merchants with the Grab Pay QR code (similar to say Alipay or WeChat pay in China but every country has their own mode of QR payment in Southeast Asia understandably). Hence it's effectively cash.

I don't believe so. We live in Singapore and have a Singapore issued Visa. We use Grab in Singapore, on arriving in Malaysia, the app automatically goes to the local app. Until last year, we could top up with our Singapore visa. Now we can't.