The only thing I really have to say is that Gaara can't manipulate Gold Dust - what he did against Gengetsu was using his own sand that his father had mixed Gold Dust into in order to form that golden egg. He simply made sure to keep the Gold Dust inside his normal sand for that concealment technique.
Now, some other things to note about Magnetism Release and Iron Sand is that it is technically neutral to all elements, though you should be cautious about Lightning Release. It will not only be conducted throughout your Iron Sand, but it will also disrupt the magnetic fields a equivalent ranks, completely rendering your Iron Sand useless.
But let's begin with something quite simple.
(Jiton: Satetsu No Jutsu) - Magnetism Release: Iron Sand Technique
Rank: D
Type: Supplementary/Attack/Defense
Range: Short-Mid
Chakra cost: 10
Damage Points: 20
Description: The user creates small weapons and defenses out of iron sand. The sand can be released from sand in the users possession or from the ground nearby.
A very simple jutsu, this allows you to draw Iron Sand either from a pouch you have, or from the environment (there's a lot more out there than you think there is) in order to form small weapons or defenses - a kunai, a fist-sized ball, a shield that you could wear on your arm, etc. Now, with this technique your magnetism only allows the Iron Sand to stick together, and won't cause it to float. The basics behind this technique, and why it's useful, is that you could create a small spike of Iron Sand on the ground as your opponent is moving, impaling their foot and causing pain. You could also create a quick shield to defend last-second against an attack. Or, if you have the customs, you could have a technique that later takes advantage of objects made of Iron Sand, and does something with them, in which case it may be better to use an Iron Sand kunai instead of a normal kunai.
So, why don't you perform the technique, while asking me any questions you may still have, and then tell me some drawbacks or general disadvantages this technique could have.