I suggest to do what your current needs are, or in the near future.
You cannot SOA enable every tiny service you have, or try to make everything into a generic service, that potentially everybody can use.
IMHO the governance of the SOA services becomes harder, as you would need to keep tight control of who is using your services, offer SLAs and whatnot. All together making maintenance more harder.
So in the future if you get a need to SOA enable a service, then you can go down the road when that happens. And at that time maybe REST is better than EJB etc. So take the battle when the time comes. EJB is IMHO not a good SOA interface, as its too Java centric, and also tight coupled with the Java interface / java types exposed in the EJB.