If you think you're on the right track get a low profile copper server heat sink and mod it into the acrylic reservoir, and wallah, you've got your copper for cold transfer.
Below is a picture of a mod I did similar with a much larger copper server heat sink and a XSPC acrylic res, it did not do the job but looked cool when finished and makes a great conversation piece.
The reason I put this thread here was to show what will work, you're experimenting with some of the same stuff I did way back that did not work.
Of course I learned everything I did the hard way, so if that's the route you want to take, you should not be cheated out of it, go for it!
Ryan, I was thinking about doing EXACTLY what you did here. How could it possibly not work? How much colder did it make the water? The only way I can see it not working (assuming you assembled it tightly) is if your TEC was dinky (which it looks like). How many watts was it? Did you consider getting a high-power TEC like the ones in camp refrigerators?
It seems to me that in your system, no matter how big your TEC is or how many amps it pulls, any and every degree of thermal delta from the TEC *will* cool the water some, no matter what.
What went wrong? Did the hot side stay hot because of a crappy fan, or what?