Let us also give Lee a little credit here; Longstreet's ideas sound good on paper but putting them into practice was another matter entirely.
First, the idea of slipping around Meade after the battle on the 1st is one fraught with peril. The first problem is you have to finish concentrating the ANV before attempting such a move, and that's just going to give Meade more time to react. Then, you have to deal with the fact that you know that some major portion of the AoP is still to the south of Gettysburg, between you and where Longstreet thinks you should be, and you have very little idea of where exactly it is. After that, you have to execute such a move with Meade standing right in front of you, and hope that he doesn't react to it before you pull it off and catch the army strung out and vulnerable.
Second, let us consider the notion of flanking the Round Tops and getting in Meade's rear. Again, a good idea on paper. But, doing it will delay an already delayed attack even further. It will also open a nice gap on the right of the Confederate line. It also presupposes that Meade will not notice or react to such a movement (and Meade is the guy with the advantage of interior lines this battle). It even further presupposes that there are no large body of Union troops behind the AoP's main line, which would be an incorrect supposition.
Lee made plenty of mistakes at Gettysburg, but turning Longstreet down wasn't one of them in either circumstance.