Just returned from Seoul - I was there with both my nephews, booked a Deluxe King room via the Amex FHR rate (three nights for two - including breakfast for two, 100$ credit on incidentals - and upgrade).

We ended up in a Grand King Corner Suite - the rollaway bed was an 65.000KRW extra per night. One of the nicest suites I had been in.

Breakfast in the lounge was okayish - limited spread, but qualitywise it was okay. - we went in the loung only because the waiting line for the restaurant breakfast was going back to the elevators on Sunday.
The next two days we went into the restaurant - we were overwhelmed with the huge buffet - more of a brunch buffet serving lots of Asian hot dishes as well. Coffee service was slow - we waited about 15 minutes for our coffee and juice - but something that we experienced at multiple spots in Seoul.

Can't comment on high tea or cocktail hour in the Exec lounge as we were exploring the city.

Would stay there again for sure.