Here's a thought you might try, using the Tamiya Flat Aluminum. I've used the shiny NMF finishes from several of the acrylic lines of other manufacturers, they look really good, but some are not as durable as I'd like. Handling can damage some while finishing assembly, decaling, etc.
I agree, the Tamiya flat aluminum is grainy and needs work. Just experimenting with it, I found the fine polishing pads work wonders by leveling the gritty look, and leaving a fine, realistic polished aluminum appearence. The level of polished look is easily adjustable, either by grit of polishing pad, or time spent buffing. It polishes easily and very quickly.
I also find that even though I customarily prime the model with Stynylrez, (I know, a strange name,) the flat aluminum works well with primer, or without.
My process is to polish to desired level, then a coat of Tamiya clear, adusting polished look by using whatever combinations of their clear finishes works. I use only their X-20A, and combinations of gloss and flat as my clear mix. My favored thinning ration is 20-30% thinner to paint.
Worth a try, I'm sold on it and continue using it. If you feel like it, let us know what you think of the results, others might want to try it.
Patrick