The Saints pull guys in off the street every year and get results d/t the passing threat.
		
		
	 
 Can you please list a few examples of guys the Saints pulled off the street that got rushing results?
		
 
		
	 
Pierre Thomas, Khiry Robinson, and Ivory himself down?
		
 
		
	 
 Pierre Thomas wasn't pulled off the street. He was an UDFA out of Illinois that started over Mikel LeShoure his senior year and beat out Saints' third round pick Antonio Pittman in camp. He's shown to be a solid runner, while a highly drafted prospect has failed.
Robinson has only had a handul of NFL carries and was only successful in one game thus far - breaking a 20 yard run - which will help your ypc on limited carries.
Using Ivory as an example to make a point about Ivory? Well that really makes very little sense.
Ivory is a solid NFL RB that can not stay healthy, but has shown to be an effective runner when he is. Saying he couldn't beat out Powell is disingenuous since he wasn't healthy during camp or during the season. Saying he makes "backup" money is a subjective statement, as he makes what he should be making for a back that has yet to prove anything in the league. 
$10MM over three seasons isn't a major commitment but it's also not insignificant.
As far as the Jets starting RB next season not being on their roster yet - time will tell. I think they want Ivory to be the starter this season and next but he'll need to show he can stay healthy and be productive.
I'm a fan of the Jets who really has no fantasy commitment to Ivory (own him in one league that's a total rebuild so I don't count on him), but he looked far better than the 3.1 ypc last week would lead one to beleive. As I stated he lost 3 yards and 4 yards on two carries in OT where it was obvious the Jets were just going to run up the middle and hope to kick a FG. He ran hard during that game, broke tackles, carried defenders and showed burst in the open field.
Powell is a solid back that can step into a few different roles, but in my opinion the Jets would prefer him to be depth and not their feature back.