I think the other thing TNA has going for it over ECW is the worldwide audience!
From what I know, ECW had a brief airing over here towards its end, but even that was on a backwater channel!
TNA (while a week behind) gets a lot of exposure as its on a channel totally devoted to wrestling (strangely called The Wrestling Channel).
With the added exposure through the internet (lets face it, the internet was nowhere near this big during ECWs days, and the net helps spread the word quicker than just about anything).
Factor in the fact people are tired of WWE and want an alternative, where as ECW was around during a time when WCW & WWE were going head to head in the ratings wars (quite possibly the most successful era for both brands).

I was always under the impression though that ECW was more mainstream than it obviously was, but maybe thats as bsams says, the Jim Morrison syndrome!

I think WWE will try to push ECW as a TNA style show, so the lucha/cruiser style would then be their answer to the X-Division!