Oh, how I wish this were all true, however I will have to say that gm made weapons do not influence accuracy.
I have a gm smith, and a gm warrior, so this whole issue has great interest for me. GM made weapons have more 'metal' in them (as you can see when you smelt them, you get more ingots back), and consequently have more durability and power. I use my top end gm weapons, and I notice the difference, as do all my friends and customers who use them. (I gave up using magic weapons ages ago).
From what I have read, made, and tested it seems that gm weapons range from durable of ruin, to substantial of might. However, the top notch weapons (i.e. the 51/51 katanas) are equivalent to 'Force'.
I smelt the low end weapons after valuing them on my vendor (e.g. katanas from 38-42gp), sell for 200 gp the katanas in the 43-48 range, and sell the 49-50 katanas for 450 gp, and the 51/51 katanas for as much as I fancy at the time. For larger weapons such as the halley I sell the top of the range gm flavour for 650. Personally I think they are worth more than this.
Top quality gm weapons are excellent, and represent great value compared to magic weapons. You also have that added bonus of not having to fear about losing a mid range expensive magic weapon that you just purchased. Grab a few top gm weapons, and wade on in there!!!
Oh, and I also make it clear on my vendor which weapons are which, and put the VDP and maximum possible value (e.g. 51/51) on the top notch ones, along with a wee little essay written in a book that is locked down on the steps of my house.
As far as making weapons above Substantial of Force, hmmm, well I've made more weapons than I've cut bandages, and I know a few smiths, and I've never heard of anyone making anything above the already established values (ok, maybe the very rare 1gp higher occasion), let alone making one significantly higher that would raise the weapon to Power/Vanquishing.
Oh, incidentally, a smith friend of mine noticed something the other day, which I also tried out. Now, this could be coincidence, or it may already be well known. Using a brand new smiths hammer when making that damn plate armour seems to work wonders on the success rate!
Happy smelting all!