Enchanting Items:
Since I’m trying to increase the ‘WOW’ factor of magic items and since you won’t be able to wander into any store in Midkemia and pick up a Flaming Sword +8, the issue of Enchanting Items needs to be addressed.
Making the players unable to get magical weapons and armor will not make +1 swords feel special. A +1 sword is boring because all it does is add a static bonus to hit and damage (well, they're slightly less boring this edition because of the crit bonus too, but still fairly meh).
You make magical items special by restricting the special stuff, and that's something that 4e already does. You can't craft something that is above your level. Since items that you find are one to four levels above that, anything you craft is likely to be pretty lacklustre.
Not to mention the fact that the DM has ALWAYS been able to make people go "oooh, ahhh" at magic items by simply handing out something that doesn't exist on the lists.
I'm not trying to rag on your idea, just point out that you might be solving a problem that doesn't really exist.
Anyway, on to critiquing the rules that you've put up:
Firstly: Why doesn't streetwise have any effect unless you go black market? Surely it should have an effect on finding legitimate sellers as well as illegitimate ones? Not to mention: usually a black market for goods that aren't illegal is not MORE expensive than the regular market...
Secondly: Doesn't this system just lead to players asking down their wish list, one item at a time until they get lucky?
"I look for a +8 flaming escutcheon"
"I look for a +8 frost escutcheon"
"I look for a +8 lightning escutcheon"
etc etc.
It means that people looking for boring stuff (like more boom) are going to get everything they want, while people looking for interesting niche items are going to miss out.
Finally, the place of power thing isn't really going to be much of a restriction: players will just make sure they go to a place of power, and whip up everything they need. The only real regulator to that is the DM restricting the players freedom constantly, and that really never makes players feel happy. I suppose if the places of power are governed by people who heavily regulate their use, then things are different, but then they either have the right to use it, or they don't... and as soon as they do, it's magic items galore!