Under what circumstances would I need a new referral letter to re-visit the same doctor?

In general, soft contact lenses are a lot more comfortable than rigid gas permeable (RGP) contact lenses. They are also much easier to fit, and can give very good vision. Both soft and RGP lenses may be suitable for many people. But each has their potential pros and cons. For example, soft contact lenses maybe a little more drying to the eye than RGPs, and for people with very high spectacle powers, sometimes soft contact lenses may not allow such a long period of wear each day because of issues with oxygen transmission with thick lenses.

There are several aspects to consider in answering this question. Firstly, there is no cure for presbyopia/'Lao Hua', which refers to the loss of autofocusing ability of the eye. There are no cures, there are only compromises. That is why, in order to get relatively good vision for far and near, some compromises have to be made for the contrast at a particular distance when compared to monofocal lenses. But then again, you have to consider what you mean by 'poorer'.