A Jeb endorsement would generate media buzz which would most likely translate into higher poll numbers.
He's already at roughly 10% in many polls. If he gets to 15% or more he's in the debates. And then his numbers will only rise even more.
Voters are already dissatisfied with both major party options.
This. The disgruntled anti-Johnsons in the LP core are already not on board. Jeb's endorsement will just give them some "I told you so" material but won't matter much really there. Amongst Paulite Rs and moderates that hate Trump? This is going to be something.