I'm not sure. (You probably know/care more about this than I do; I assume everything can be done under NSL already, or entirely internal to large companies or their existing business partners, or by criminal organizations, so the legal protections are largely irrelevant.)
I assume by ECPA you mean "ECPA as modified by the Patriot Act", which is a substantial change in protections. Under ECPA as originally enacted, a great many things currently done would be illegal.
However, there's at least one major area which is currently illegal but would become lawful under CISPA:
Providing classified intelligence to private companies in violation of the NSA of 1947 (which I don't think is permitted by ECPA; ECPA just allows info to go from private company to government in ways which would otherwise be wiretap act violations without specific court orders). Couple this with the government enjoying overclassifying everything, and it's a problem.
I don't really have a problem with this, except that the procedures and safeguards need to be built well to protect that information. I think they can do this.
The other addition is that intellectual property is covered. If "theft of [...] private information, intellectual property ..." provides "exemption from all liability [...] acting in good faith", this would seem to allow private entities to do a lot of things. I don't think ECPA/Patriot gives those powers to private entities, so a provider could have one (badly written) legal contract with customers (violation of which might lead to civil liability), then invoke CISPA to violate it. Most contracts are written to permit information sharing for security issues, but adding copyright protection would greatly expand their scope. I think it would allow a copyright holder to request (with no legal basis) information from an ISP, including ECPA protected information like VOIP/email in transit/etc., and or the ISP to turn it over with no legal protections to the requestor.
So, overall:
The Lungren (http://www.govtrack.us/congress/bills/112/hr3674) HR 3674 does not have this feature/defect. I'd support Lungren as written.