The only problem is that without the System state data the files you restore will loose all of their original rights assigments. Depending on the amout of data you are talking about and the number of people accessing the data that may not be an issue.
In a disaster situation you are assuming tha the orininal server is gone or at least inaccesible for a long period of time. Because of this you want the System State information. It makes the process of restoring the computer to it's original state much easier. System state holds registry, security, and network information. The system state is part of the restore that makes the restored computer and every other service on the network think that this is the opriginal.
You want your replacement, in most situations, to act just like the original. In a disaster there original is gone so there is no need to worry about conflict on the network with the restored machine.
If all you have are user directories on this machine then by all means just get the data. However, I would at least capture the system state in each backup job just in case you decide you need it.
