I get about the same number of fire geodes on Firesday as I get any other type on the respective day with no weather, so 1-2 in the whole day, occasionally I get none in the whole day, regardless of the type. The lack of fire weather, not the drop rate is the problem. As far as I've seen, they work exactly like every other geode under the same conditions.

However, rarity isn't the issue. Take a look at the AH history. Flame Geodes are consistently one of the most common type on the AH and they are still the most expensive by a long shot. Yes, they are harder to get, but people farm them because they are so expensive.

The issue is with demand. Fire weapons are too consistently useful to too many jobs, while most of the other elements are only useful to a few jobs, and, even then, might only be useful for very specific situations that everyone that plays that job might not encounter. The only way to fix the prices is to make the other elemental weapons more appealing. If more jobs had viable options other than fire, the price would go down on flame geodes because not every other person would go for them.

Even if they increased the amount of fire weather, I really doubt the price would come down. The current supply is mostly coming from people that specifically farm them. Unless fire weather was absolutely everywhere, the price isn't going to drop much. If the price isn't high enough to motivate people to specifically try to get them to sell, then they are going to become rare, which will keep the price up. The stable price point might go a little lower, but I doubt by that much.