Alright I ended up staying at the Ivy so I'll post my review from the perspective of the AMEX plat FHR program (as I probably wouldn't have booked otherwise):

1. Basic room upgrade, when available: Couldn't tell. Higher floor; view is nothing to write home about, but could be more the location than the hotel. Room was nice!
2. Early check in when available/ late check out 4pm: Done (10 am) and done.
3. Free breakfast --- this was $30 per person ($60 total) for either the Italian restaurant (for breakfast it's 100% American style food) or room service or the lobby bar. It was mother's day so the wait for food was huge at the restaurant. AND .. a bit overpriced for what it was. But hey, it was free, I suppose!
4. $100 credit at the spa. Massages were all booked but pricey (closer to $200 tax and tip) -- can also use the credit at the Spa store (tons of serums, bath products, robes, etc) or the Quartz Spa ($50 a person --- a very fancy hot tub, showers, and a sauna). I don't think I'd pay $50 for this either typically --- but as some kind of free benefit, why not. I was also hungover so this was nice for that

Oh the hotel also brought up (unexpectedly) a free plate of fruit and trail mix about 30 minutes after arrival. Not bad. Awkward timing but I'll take it.
The gym was also top of the line. Power racks, rowing machines, and some very fancy "curved" treadmills that are sort of self-powered? (and traditional ones). Free fruit and water everywhere.

Altogether very nice --- front desk person mentioned the benefits upon arrival so--- you didn't feel like you were hounding them for it or something. No BS. I'd definitely go back.