I know it's probably wrong, but I've taken to hoarding gems towards the end of BG1 so that I can sell them at the beginning of SoD and cash in after my gold gets stolen. With the amount of high value gems in the late game, you can easily have enough to replenish most of your gold in SoD, and in BG1, you eventually hit a point where you have stupid amounts of gold.
There is some justification for this. In old school PnP, gold had weight, and couldn't lug a massive hoard. You either had to put it in a bank (and trust the DM not to screw you over and have the banker abscond with your cash), or invest it in some gems and jewelry that were light weight, but high value.