The Jets are in a position where they have to stick with Sanchez; as bad as he is Tebow would be worse. And if they do make the switch to Tebow once he bombs they're stuck with Tebow because they won't be able to put Sanchez back in. The other issue is that the package for Tebow at QB is just a fraction of the Jets total package that Sanchez draws from. Mike McCoy developed an offense around Tim Tebow in Denver that led to success. Tony Sporano has not had to do the same thing in New York, they are not prepared to put Tebow at QB.
The other issue is there are only two QB's worth drafting at or near the top of the draft, Geno Smith and Matt Barkley. And both of them have huge question marks.
I think they should definitely try to upgrade the skill positions on offense (RB, WR) because they do not have quality talent at those positions. And most of all they should fire Rex Ryan. He's a like Sanchez in a way, somewhat overrated and better suited to be a backup (or in his case a defensive coordinator).