To andrea for certain types of data and certain types of business encryption is required on all media.
The DMVPN is designed exactly for encryption on a mpls network. Your need for DMVPN will depend on how you data flows. If you data is all hub and spoke with no data between the spokes then a manual gre tunnel solution will be simpler to set up. But if your data flows like this then you really shouldn't be paying for MPLS in the first place.
I'm not sure if you can run a multipoint ipsec configuration without tunnels. Most the time this requirement is because of the need to carry routing protcols.
DMVPN is mostly to make your life easier. You could setup a full mesh of tunnels but it will depend on the number of endpoint. Even when you start thinking about how much configuration of ipsec and gre is involved with only say 5 nodes to run a full mesh it becomes a pain. Since DMVPN only creates the connections when they are used it should reduce the load on the routers if you assume you do not have any to any traffic runn all the time.
DMVPN and the NHRP stuff takes a little while to get used to when you are troubleshooting things but it is much simpler than full manual configurations in a large network
