I think it would be just as foolish to dismiss this outright, considering the " tantalizing hints that there may be something to it" and the developing theories as it would be to start dumping your life savings into Rossi's company.
No, not really. It's the "tantalizing hints that there may be something to it" part which pretty much screams bullshit. Fusion is not exactly subtle; if it's going on, it's not hard to detect, and hasn't been. Furthermore, according to the Wikipedia link, the device was covered up during demonstrations, actively hindering any kind of measurements. Add those together and shave with Occam's razor, and you get "conman".
Also, fusion is not really all that hard to achieve. For example, a fusor is simple enough for a hobbyist project. What's hard is a fusion device with a net energy output; we don't even know if Rossi's device is doing fusion at all, so why would we even begin to assume it's not only doing so but generating more power than it consumes?
So yeah, with the information we have, this seems like exactly the kind of thing that should be dismissed outright.