Add a couple of cultures and religions that diversify the else.

Such as
High elves
Wood elves
Dark elves

Give each type of elf it's own look It don't culture it's only religion and one or two unique units.

Such as the wood elves would have archers
How else could have horseback me dark elves get out melee fighters.

If you look at the Lord of the Ring add-on it adds a bunch of types of units You could split these units up amongst the races of elves so there's some diversity.

Of course you could always make more than three but those are like the three prime types of elves.

You can also have night elves, aquatic elves, Fey elves, but going overboard is not necessary just three unique ways to play them would be sufficient as those are the three primary found it almost every medium.

But obviously their cultures and religions would equally be different.

High elves are more religious and technology focus

What else are more isolated and nature focus

Dark elves are more military focused and fanatical