I recently came across ExtJS and I am quite impress with the features that comes with it

I have a number of existing web applications that are form based and I thought it be good to add a bit life to them by adding ExtJS (i.e. validation, messages etc) and was wondering whether its best to rewrite the page or try updating the pages to include ExtJS??

My applications are struts based and in need of a lift and ExtJS looks like the right way to go.