Given the limited acceptance of AMEX in general, what are the best places to use the AMEX SIA KrisFlyer Credit Card?

Hotels, restaurants, most online sites accept amex now

To me, with the fact that my miles are credit to KF and start their 3 year expiry once I start spending on this card, I would only use this card if I knew I had an upcoming redemption.

As you have mentioned, a $1K spend is quite achieveable, but the problem comes when your 10K miles sit in your FFP and can't be used to redeem anything, unless you can spend your way up to a decent number of miles within 3 years.

I would use the $1K spend as a way to get 10K miles if I was just short of a redemption that I had in mind (and with miles from other cards already primed for transfer into KF), or, if I had big spend coming up and wanted to get the bigger bonus of 37K miles.