I don't think that ECW would have lasted long-term, no matter what. Vince only did it to eventually trash ECW (since people at shows were chanting "ECW") , so he tried to make it as bad as possible, so that the Universe would forget about it. "December To Dismember" is a perfect example of this. Also, the most time the ECW Title got at a "Wrestlemania" was an 8-second match between Chavo Guerrero and Kane. ECW didn't have a chance.
I believe that Benoit was moved to ECW for a number of reasons:-
(a) he was a former ECW star, so would be accepted by ECW fans
(b) ECW had two distinct types of wrestlers at the time, either good wrestlers, but who were green (C.M. Punk, John Morrison), or older, crappy wrestlers (E.G. Boogeyman, Big Daddy V). I guess they thought that benoit would be able to teach the young up-and-comers a few pointers in the ring, and graft good matches out of the older guys. So, he was like in a Finlay role, a veteran who is used to get others over. Apparently, the new contract he signed with the WWE was for five years, but had a clause where, if he chose to retire, he would serve the rest as a trainer or road agent. So, this was probably preparation for that. So, ultimately, I think they had Benoit down to train others, like Goldust, Finlay, Ricky Steamboat and Dean Malenko do. If he had lived, and not done his crimes, I think he would have fitted that role nicely.
(c) I have heard that Benoit was out of contract, and TNA were making a sizable offer for him to jump ship. Maybe one of the things Benoit wanted to stay with WWE was a World Title. Vince probably promised him this, but tricked him by planning to put the ECW WORLD Title on him. Maybe Vince didn't think that Benoit's run as World Champ didn't rate last time, so put the ECW Title on him, to stick to the demands of the contract, but give him a "D" grade title, so as not to lose ratings on "Raw" or "Smackdown".
Amongst all the obvious reasons I wish Benoit had not done what he did, it meant that we never got to see a Chris Benoit v C.M. Punk match, which would have been a good match.