craft a manufactured item? Does the item disappear when the created materials vanish?
Yes, you could, but yes it would disapear once the spell duration is gone. So it mostly won't last long enough for you to actually craft the item, unless it is either vegetal or mineral matter.
By RAW, you can't even use the Fabricate spell to increase it's durability, because the spell has a original material as a material component.
craft magic items? Does the magic vanish with the materials?
The costs to create magical items says:
Cost: This is the cost in gold pieces to create the item. Generally this cost is equal to half the price of an item, but additional material components might increase this number. the cost to create includes the costs derived from the base cost plus the costs of the components.
So, we can see that magical item crafting also requires magical components, which cannot be replicated by the spells. And we don't know how much of it is magical in nature, so you are in GM's fiat territory here. We do know that some of it is magical.
Unless said magical item is not part of the magical ability cost, such as adamantine to create a +1 adamantine sword. The duration is prohibitive though, but creating a +1 Wooden Shield should be last enough for a single day of use, though thats a waste of the (magical) material components (500 gp in this case).
You could probbaly use the spell to create the raw material to craft a homunculus, but that would only save you 50gp at most, and unnecessarily reduce it's usefulness. Otherwise, it follows the same rules for magical creation (see above).
craft a one-use magic item, like an ability enhancement tome and use it before it vanishes?
There is no difference between a permanent magic item or a one-use magic item, other than their relative cost and usefulness.
use it in experiments to create a new spell to reduce its cost?
In general, the costs of magical research are related to magical components, special inks or another rare ingredients. So you cannot do that either.
However, using the Downtime Rules, you could probably convince your GM to allow you to create Goods using those spells, which could be used on your research on a daily basis.
Assuming this is done by a wizard/sorcerer of at least 15th level (or cleric
with the necessary domains), your best bet to create actual permanent materials would be casting a Wall of Iron (or a similar spell), then transmute it using Polymorph Any Object. Both spells are either instantaneous or can become permanent, so you are actually creating matter from nothing, and neither spells has a restriction on the use of this matter.