Even though there clearly are a lot of advantages that you will get when you get your Singapore PR application approved, there may still be some downsides to it, depending on what you value most.
First of all, while it can allow you to be eligible to purchase more types of properties than foreigners can buy, there are still some classes or categories of real estate which you may not be eligible to buy as a PR such as that of a first hand HDB or certain types of condominiums. The amount of property taxes you will be required to pay will be significantly less than that of a foreigner already, but still slightly more than that of a full citizen.
Second of all, if you have lots of desire to want to vote during Elections in Singapore, then unfortunately, as a PR, you do not have said voting rights. Only a full citizen above the age of 21 years of age will be allowed to do so.
Third of all, a PR would not be able to make use of the Community Health Assist Scheme (CHAS) which is a scheme that allows people to have subsidies for selected medical appointments or treatments. Nobody really wants to be able to make use of this CHAS – after all, it would mean that you are medically sick if you are required to use it. However, it is a good additional advantage applicable to citizens only.
As you can tell from the above, it really depends on what you hold as more important to you. If the above are non-consideration factors for you, then you really can just stay as a PR, and not need to change to get a full citizenship, as that would be unnecessary trouble, money and time required for you. Additionally, one of the things about Singapore is that there is no dual citizenship legally allowed. This means that if you decide to convert to a citizen, you cannot easily change it. However, a PR gives you a great deal of flexibility still.