This is why there are sooo many different monsters for D&D. All DMs want to surprise players every now and then.
I have no problem with you altering monsters in an adhoc way for 3.5. If you are an experienced DM then you don't need the EL crutch anyway. Since you have greatly reduced xp for slaying then the accurately adjusting the CR given your changes is also not as important.
One way to keep players on their feet is to change the descriptions of monsters.
I've also been thinking of adding some weaknesses and features to the elementals to spice them up a bit (but each elemental would be slightly different).
One trope in fantasy is that the Hero(es) defeat the monster by finding its weakness. This sounds like it would fit in with what you are trying to capture flavorwise. You may wan't to allow reasearch and knowledge checks to find the weakness, or Spot checks and something else while actually fighting the creature. If you want mechanics for doing this the 4e skill challenge may fit the bill.
I have no problem with you altering monsters in an adhoc way for 3.5. If you are an experienced DM then you don't need the EL crutch anyway. Since you have greatly reduced xp for slaying then the accurately adjusting the CR given your changes is also not as important.
One way to keep players on their feet is to change the descriptions of monsters.
I've also been thinking of adding some weaknesses and features to the elementals to spice them up a bit (but each elemental would be slightly different).
One trope in fantasy is that the Hero(es) defeat the monster by finding its weakness. This sounds like it would fit in with what you are trying to capture flavorwise. You may wan't to allow reasearch and knowledge checks to find the weakness, or Spot checks and something else while actually fighting the creature. If you want mechanics for doing this the 4e skill challenge may fit the bill.