It may be beneficial to put some insulation under the sump in the winter but what about the summer? In the summer, you will benefit greatly from having a sump that is directly on the concrete. Not sure how much work is involved in draining your sump and sliding some insulation under it. If it isn't "too" much work I would cut your return pipe and install unions that are about 12" apart. Then make one PVC piece with unions at each end that will fit when the sump has insulation under it. Also, make another section that will fit when there is no insulation under the sump. Then you can switch out the insulation in the spring/fall and pop in the required return section. That would be your best bet in regards to electricity.
Your easiest route would be to throw another heater on the tank. But I like to keep the heaters on my tank to a minimum unless you are controlling them with a separate digital controller. Heaters can stick on and you don't want to have too much heating power on the tank to the point that it can quickly overheat.
I have noticed that my CO2 rate to my reactor DOES vary drastically when the room gets cold. There was one night this past fall that a cold front came in. I still had the fans in the windows as it wasn't too cold outside that I needed to close up the window. Anyways, the cold front came with some strong wind that was blowing cold air right into the fish room. I went down to check on the tank and was caught off guard at how cold it was in there. I looked at my bubble counter and noticed that the bubble rate had almost doubled. I left it as it was. I closed up the window to the room. By morning, it was room temp in there and the bubble rate was back to normal.
There a couple different solutions to avoid this:
1)Place the CO2 tank remotely in a room where the temperature stays more stable than in the basement.
2)Use a ph controller to control the CO2. I will probably go this route myself. The mini reactor you are getting from Kevin already has the probe holder so you would just need the controller and you would be good to go. About the cheapest you will get a decent controller for is a Milwaukee from DIYreef.com.
BTW, I just finished reading that hijacked thread. Took a while as the posts were long. Interesting discussion, however.