Instead of shooting the entire Guitar, you might think about just showing the bottom half, in a "close-up" shot, so that the beautiful wood is shown in detail. This would put the emphasis on the wood grain and the finish as well as the hardware. The 3200 would do a really good job of this. You might want to think about using the 18-55 for the close-up, or crop down to a close view of the wood. Getting the right angle with the flash, as you know, would be important. A shot outside on a nice day would do justice to the wood for an image...might be worth a try.
It looks like you used the 50 1.8 for this, F8, ISO 200, 1/60 (with onboard flash?), in Aperture mode. To a a rookie like me, that all looks like it should work. As noted, if you would have isolated the Guitar from everything else, it would have emphasized the Guitar more. Possibly, if the Guitar was raised up at the top end a little more, you might be able to see the wood better. I think the image is pretty good, considering.
Keep in mind, this is only my opinion.
It is obvious you have a beautiful instrument, and I don't even know anything about Guitars!
You have an excellent camera, as you know. I will look forward to seeing more of your pictures.