I personally really enjoy Celadon- don't have a bad report to give. In January, I was on a flight with a guy to Bangkok who had actually planned an overnight at Bangkok just so he could have dinner at Celadon. Impressive...
As for afternoon tea, it is not really my thing- but I understand the Pens is just as good as the Oriental (perhaps you can get a better opinion from an afternoon tea lover).
Spice Market is nothing special- at least I don't think it stands out as being exceptional. Please do post if you decide to go there and you believe it has improved.