Aside from providing naturally better stamina control due to becoming as natural as their base state and allowing them to likewise control the amount of power they output far better, I wouldn't say so. There doesn't seem to be anything supporting an increased multiplier or anything of the sort, considering what guidebooks have to say on SS2's boost and the idea of it being able to output more power than the grade forms in general not really lining up with the point of mastering SSJ, plus (for what it's worth at this point), Toriyama's BoG interviews about Galu needing to strengthen his base and SSJ forms instead of using SS2 and 3 would suggest that this wasn't a part of his mastery of SSJ in the Cell Arc.