To some extent, Bitcoin's price is effected by altcoins'. If altcoins disappear, Bitcoin's price would be higher. More money will stay at bitcoin! No shitcoins, no dump and pump, it will be good for the image of bitcoin!
The Paycoin IPO must have generated a fortune in Bitcoins for the dev, and those Bitcoins getting dumped were probably one of the reasons Bitcoin's price crashed on completion of the IPO. Alt coins with massive volume can seriously affect Bitcoin if there is a massive dump of them.