If you have Flaming on a weapon, it affects only that weapon. Likewise, if you have Speed on a weapon it affects only that weapon. The fact that it says it doesn't benefit from similar effects such as Haste is basically there to prevent getting lots of extra attacks on that weapon.
The supposed RAW answer of two Speed weapons not allowing the extra attack with each one is BS. Even if it's intended to work such that multiple weapons with the enchantment only grant one extra attack total, it'd be a slap to the face for TWF (and your coffers!)
yup. I have to agree with this. It is illogical to think a Speed weapon in each hand would invoke any stacking consideration. The weapon isn't casting a "Speed" spell on the wielder so I see no reason to disallow an extra attack with each weapon.