This problem seems like it could be easily fixed. There should be a way of using an algorithm to ensure that eventually chests are more likely to open higher level gear. It could be a function of total gold spent, or total time spent playing, or the average level of all your classes.
I completely second the above comments. The balance of the game seems to be buying one large chest after about 2-3 missions, and this is fine, but if you only get a relevant item after about 20 chests, then the rate is much too slow.
If Bioware wants to make this more of a cash cow, an alternative arrangement is to have something like a "Rare Chest", which only contains 3 blue or higher items, and no potions, and cost it at, say, 10,000 gold (hell, even 20,000 gold would be an improvement). That would give people something to work towards, and opening one would be a real event.
A third idea would be to have class-specific chests, e.g. a "Soldier's Chest", "Thieves' Chest", "Arcane Chest", with relevant items specific for that class pitched to the average levels of your kits.
Having a basic "big chest" that has no relation to how long you've been playing seems like a simplistic and lazy way of handling loot, when it could have been far more interesting and rewarding without necessarily yielding less revenue.