I wouldn't recommend:

  $obj->new(...) ;
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either. And, if I ever wanted to have a new object of the same class as another I'd prefer:

  ref($obj)->new(...) ;
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because (once you've worked out WTF is happening) it says exactly what is intended.

However, on the general basis "Be strict in what you send, but generous in what you receive", throwing a run-time error at $obj->new(...) strikes me as ungenerous. Noting that perlobj for 5.10 (and 5.8.8) describes how to cope with this eventuality -- as the fourth in a sequence of increasingly complete object constructors.