If you are happy with what you have in regard to performance and features, then indeed no, you do not need it. The firmware itself brings the usual offerings of UI improvements, performance tweaks and general glitter of being a large step up from the GB firmware. As I root and try different roms, I've used many variations of it already and in general like how it behaves on my Galaxy S2. It's best to remember that ICS is the new kid on the block and will take some time and future updates for it to be seen as smooth and established as Gingerbread is. It stands to reason as GB has had a lot of time to be polished up.
As for actual interface benefits, probably best to check a feature list as some things will interest some folks more than others. Bear in mind a selection of newer apps may be specifically designed to only work with ICS such as Google chrome browser. As time goes on more may develop this way. If you like the latest apps it's something to bear in mind.
As always it's subjective if you actually need to upgrade.