Big thanks to reader RWHR for this amazing datapoint regarding the SPG Lux:
It worked on $300 gift card at hotel front desk. It triggered the $300 credit plus it triggered the $60/$300 promotion I had added to the account as a sweet bonus! I bought gift card on Monday. $60 credit showed up on Thursday and $300 credit on Saturday
For those that were wondering how the SPG Lux $300 credit works, we have used it successfully for room rates, in room dining while staying on points, and now for a gift card bought at the front desk. This may very well be a huge money making card. I suggest every AD get the Lux and then the personal SPG with the intention of upgrading the Personal SPG version to the Lux. This would mean $600 in credit as well as 2 free nights a year.
I have exhausted my credits for the year but this offer of $60 for $300 spend might still be good for a gift card, even if I cant double dip it:
Again, thanks for the data points out there! Keep them coming on the comments below!