Better practice to develop a new product based on an old project?

It is not a good idea from the view of me, a developer, to do this. As you may image the disappointment of our team when the PMs decide to develop a 'new' product based on our project 3~4 yeas ago, which used old techniques, such as struts 1.3, swing, etc. But we have to do this. ("rewriting the project using current techniques is slow, and under high risk") How can to raise the morale of our team and improve the productivities of the development? any one have the experience?