So far, the Goku in this game is more "Goku" than any other featured in a Smash-Like game (including JUS). This is thanks in part to his very excellent U-Air and his D-Spec in Kai-o Ken.
However, there are some last few changes that I would like to recommend to make him as "Goku" as can be without the need for any new sprites. Don't worry; I won't try to make him god-tier again or anything.
First off, his N-Air.
It's fine right now, but it's too plain. It's basically just a glorified version of that sex kick that you see on every character in the original Smash.
What I suggest is changing it to a double kick, almost exactly like C.Falcon's N-Air.
The first kick can have the exact same animation as his F-Throw and the second kick could have his B-Air animation, only reversed to face the front, obviously.
When in Kai-o Ken, it could work similarly to Fox's F-Air and Snake's N-Air, only a bit shorter, with only three kicks. The first two kicks could have the same animation as listed before, but for the third he could use his F-Tilt animation. To finish it off, have him end it with a hammer fist. The animation used for this one should be obvious. So it wouldn't overshadow his U-Air, the knockback on the hammer fist could be less than his U-Air's elbow, making it less of a spike and more of a weak downward smash.
Secondly, his f-throw. No, there's nothing wrong with it in his base form. However, I think it should be a bit more flashy when in Kai-o Ken.
It would be a 3-hit combo, with all three attacks adding up to slightly more damage than his base form's F-Throw, but having the same knockback on the final blow.
The first hit would be a straight left punch, then the second, a side kick, then a knee to the stomach for the third.
The punch would have the same animation as the first move in his jab combo, the side kick would use the animation used for the last move in his jab combo, and the knee would use the same animation as his F-Throw in base form.
Finally, his Kai-o Ken final Smash. Now, this would actually WOULD require some new sprites, truth be told, but you could rip them straight from Choujin's Super Saiyan Goku M.U.G.E.N. character, just like Goku, so they shouldn't be too hard to obtain.
Now, on with the recommendations.
So, he obviously turns Super Saiyan, and uses his Dragon Fist. Okay, fine, but it doesn't really incorporate his Super Saiyan might.
Why not have him dash forward first like his Final Smash in base form, then start executing a few rapid punches? Then, he could teleport around a fixed space with his opponent, rapidly punching and kicking them for about three whole seconds(the space is about two thirds the width of Final Destination high and wide). Again, like his base form's Final Smash, these are simply for aesthetic purposes and do not cause any actual damage. Any other enemies caught in the crossfire do get damaged, though, with a small bit of knockback and a damage count of five percent.
Once this is finished, he hammer fists his opponent over the center of the stage, then he teleports below them and powers up (the opponent should fall through the stage's platforms during the hammer fist, to avoid glitching on stages such as Battlefield).
When this happens, the gameplay should freeze during the animation to show the player what is happening. Finally, he dashes upwards and finishes off the opponent with an rising Dragon Fist (the animation could be the same as the current Dragon Fist animation, only tilted so he rises upward instead of rushing horizontally).
Well, that last part was much larger than I thought it would be.
I really hope this doesn't seem too intimidating of a task, as I think it would go miles in helping to tap into Goku's hidden moveset potential. In reality, you'd only actually have to change three things, and though one is rather large, it would be SPECTACULAR, while not actually being too cheap (it's the same as the original, only directly targeting one individual enemy instead of multiple and is MUCH flashier).
Should you see this through, I can GUARANTEE a Goku with a true blend of DBZ and SSB gameplay.
These are only recommendations, but I have seen what you can do, and am fully confident in your abilities. Even if you could only put in one of these changes, I would be pleased, but I don't think you'll have to resort to that.
If I've posted this in the wrong place, please forgive me and direct me to the right location as I delete this post, rewrite it there, and silently curse myself for my ignorance.