Unfortunately, my guess is simply increasing the refresh time is only going to solve one problem. I'm not an expert on DRAM or anything but it seems to behave like a capacitor. Longer refresh times require larger capacitance. Large capacitance doesn't necessarily mean more power, but I think it would take more voltage to change the state of a bit (you'd have to reverse a larger charge).
Also, the biggest problem with DRAM these days is speed (reads/writes per second). The best way to increase speed (without also increasing voltage, and thus power) is to decrease capacitance since discharging a smaller charge is faster -- not to mention it would generate less heat, which leads to higher density and higher speeds, which is what the DRAM market is really after.