Whats the point?
People will try to get to max level anyways. The max level market will have much more volume then all lower level markets combined (thats somewhat your point 1).
Older player will know the prices at max level. Their understanding of the prices will dominate the market. Whenever an older player levels up a new character, he will simply buy cheap items along the way to max level, effectively making money of new players who not yet know the values of their items, while not touching overpriced items anyways.
The only thing this does is creating akward and frustrating situations. If items are cheaper at low levels, people will start leveling up new characters to buy low items from low level markets, level them up to max level and sell items there. It will also create "hoarder" mentality in which you hoard items instead of selling them, since you get more at max level.
If items are more expensive at low levels, you only screw new players.
And if prices are the same, whats the justifications for a fragmented market in the first place?
However, despite the above, there will still be X sold, as buying/selling makes it easier for the player to level up.
How is that? Do you get experience for market transactions? That would be a nightmare to balance.
And if you make money quite scarce so that selling stuff would allow you to buy better gear and level easier up, then thats great. but who could possibly buy that stuff? Low level markets would be full off stuff nobody has money to buy.
Therefore, there will be an inflation curve, where gold will be worth less and less on each level.
Yes. however, you can achieve that more easily. Simple increase gold rewards with level. Max level player will get more gold, so its worth less for them.
Inflation over time will occur faster at level 20 than at level 1.
Not exactly. Since the max level market will dominate all prices anyways (people will hold onto items to sell at max level), the prices at low levels will slowly follow suit. All you accomplish is that low level players can buy less and less stuff over time since there is no transfer of money from the top down.
You need the ability for low level players to sell to high level players, since they are the ones that have gold to spend and low level players are the ones who need it the most. Same with hardcore / casual players. You can't make players stop getting money or spending it. the goal should be to distribute the gold that is made...
So in short, I don't see how most of your assumptions would actually come true.