The biggest problem you will have is NOT getting a taxi in that part of the world. The 'tuk tuk' drivers are constantly pulling up along side you as you walk along 'beeping their horns' to invite you on board. As for excursions, you get one whether you want one or not, as they stop at every family members jewellery, carpet, leather, batik shop along the way. That's a great cruise on a great little ship & still gets great reviews. If your not aware, SS Gemini is the twin sister to Freds Braemar. Regards. Wilba.
My wife and I cruised on Superstar Virgo doing a similar cruise but it excluded Krabi and Langkawi. Port Klang is probably the only place where it is better to take the ships excursion to KL. The city is a fair distance away and the trip incuded a tour, going up a tower etc, etc. More importantly being organised by the ship they made sure we were on time getting back. All the other ports of call were fine for DIY excursions. However we did one other ships excursion while at Phuket - that was to 007 Island. It included a coach trip to catch a boat that took us cruising through the small Islands to reach James Bond Island. A really pleasant day.
Have a great trip - .
Very easy to DIY if you only go to this site that I direct every one to - Try google and 'cruise ports call boards' - the first result will give you all the info under the Asia section .