Yes it would.
SPDY is a more efficient protocol than HTTP. The main benefits that you will get for SOAP/REST communication are the fact that SPDY can do HTTP header compression, reducing bandwidth, and multiplexing - that is being able to send multiple requests on the same physical connection.
For a SOAP/REST use case you will not benefit of the big performance boost that SPDY Push gives (see demo video), but it will be worth nonetheless.
Jetty is a Java Server that supports SPDY.