Windows SP1 is not required however it is HIGHLY RECOMMENDED.
Some updates will not be possible unless you have SP1 first. There is also a lot of programs that sometimes required SP1. Besides a lot of the updates only help in the later road. There has been many times when a user is experiencing problems and i come to find out his OS is not updated. After the updates are downloaded and completed what do you know, the program is working like it's suppose to be.
It is entirely your choice.