So you think that Twilight became so successfull because they simply copied?
I´d rather guess they became so successfull because they delivered something new (well, not new like in "nothing even remotely similar ever existed", more like in "a new mixture of known elements").
Vamp-Diaries seems to have been able to ride the shockwave that Twilight triggered but such things never last for long.
The best recipe for a huge success might be innovation.
Of course, clearing your own path involves much greater immediate risks, but at least in the long run it will possibly be more rewarding.
Ah ha ha ha ha ha ha.... and no to the first. Stephenie Myers was a hit because she delivered stock characters anyone and everyone could associate to in simple language. Reading it was smashingly easy.... as long as you could hold down your lunch after she spluttered "OH MY GOD EDWARD IS SOOOOOOOOOOOOOOOOOO HOT" for the billionth time.
Innovation doesn't mean sales. See Mirror's Edge. Also, TS Eliott: "Mediocre writers borrow. Great writers steal." Or Picasso (or Banksy): "The bad artists imitate, the great artists steal." And lastly, who's remembered more: Edison (or Westinghouse, even) or Tesla?
And actually Vamp. Diaries has been going strong since 1991.... so... I think it will survive Twilight. See wiki for more.