Hi, Squidhead
You can walk down to ChitLom BTS station from Grand hotel(quite a distance though ard 15min) and take BTS to Asok, then transfer to Sukhumvit MRT station and travel down to Lumphini MRT station, right in front of Lumphini station is Suam Night Market.
I enjoy my visit to the Grand Palace and Wat Pra Keow (Temple of Emerald Buddha)and Wat Pho, from there u can take a tuk tuk or taxi down to Yaowarat(Chinatown) and shop at Sampeng Lane market and eat at the Chinese restaurant there.
You can use the half day city tour to go Grand Place and Wat Pra Keow and Wat Pho there. Save the trouble of taking boat, however i really enjoy taking the boat, u can enjoy the breeze and watch those scenery and buildings.
Be very careful of those ppl coming up to u being very friendly and wish to be your guide or wanted to bring u to friends' shop to see see. No No, they are the CHEATS!!! Just ignore them and pretend u dun know wat they saying.
Just to share, i had this encounter when i going from Grand Palace to Wat Pho, this Thai man followed my husband and I for quite a while after we ignored him, then we went buy some drinks from the nearby store, he pretend to be walking around, when we approaching Wat Pho, he trying to cheat us saying the entrance is not this side, is at the other side. Lucky we ignore him totally and just walk forward, didn't know wat will happen to us if we listen to him. If you got hp with you, you can call 1155(Tourist police) if you find someone keep pestering you.
Always ask for meter fare when taking taxi, before you get into the taxi, say your destination and ask if it's on meter, and let the guy enter the taxi first, then the ladies(for safety precautions). However i realised most of their taxi drivers are good ppl, just dun hire those parked their taxi at road side waiting for passengers type, cause they will keep persuading u to go wat souvenirs shops or restaurants, trying to cheat your money.
Tuk Tuk you have to negotiate the price first, only take for short distance (ard 50bahts - 70bahts)
Be generous with your tips if you think they're good.
BTS is very convenient, do make use of that when you travel ard. Dun flash too much cash in front of alot ppl, you dun know who is watching u. be polite when you go shopping and you realised they will be good to you too.
I saw a group of S'poreans at chatuchak market keep bargaining the price so demandingly, knowing the price is very low liao and keep giving bad comments of the shop ppl like they so rude la, blah blah blah.... No surprise u will see the shop ppl faces turn black la, if for me, i'll chase them again. Thai ppl are nice ppl, be nice to them and you receive nice treatment in return.