Yes, you're still able to get the treasure chests after investing. A good way to do it is, go at the 12 server time spawning of the chests, and talk to the NPC and do the commerce and safeguard (emp HP if it matters to you) and then go to the inside treasure room. The investment kicks in after the next day.
There's also a guild skill that gives you an extra 1 possibly 2 bonus points to investment in commerce.
You can invest 2 points normally, per day, and get the bonus from the guild skill.
It starts off small, being like 80k for the first one, and the 2nd point costs more, like 100k. I know that at 22econ and what not the prices start going to 1.5ishm per nite or so, at 93 it was like 3-4m.
Sorry, don't check forums a whole lot anymore.