IMHO the GTHQ isn't completely broken but could use some serious improvement. First of all I agree with the the idea of different market place types IE: specialty / manufactured etc. I am not sure who or where I first seen this suggestion, not that it really matters. Although it is a good suggestion. Most of the time I feel that the lack of expansion/specialty items is intentional on the part of EA to force players to use REAL MONEY to buy the items. I have no idea how the random item generator works in the GTHQ but I assume it looks at what you need and gives you 0 to very few of what you need. Then when you are lucky enough to find one 95% of the time it is gone by the time the neighboring city loads.
That brings me to the other frustrating thing about the GTHQ is that after the December update the city load time has at least tripled. As a matter of fact I have even updated to a more powerful device and the load time for most cities is 15 to 45 seconds. so by the time cities load the items are long gone. So in retrospect I would say not having wait for cities to load would be a great thing with the option to go visiting other cities like suggested previously.
Just my two cents