First, one should divide all 'racial' traits into those that are truly innate to the species and those that are instead culturally derived.
Then, the core traits of the elven species should remain the same, while various elven cultures can be defined through changes to the culturally derived traits.
Drow, in some respects, is a true sub-race, for they have been so long apart from the elven people (in terms of interbreeding) that they have developed in a differing direction from their surface world kin. This does not take into affect alterations brought about via direct divine intervention, of course, which would further deviate the drow from their surface kin. As they can still breed with surface elves (some stories giving evidence of this), it suggests that they are not yet a totally different species.
So, if the species have been somehow prevented from breeding with each other for thousands of years (if not longer), then they merit differing racial traits. Cultural traits can be used to define any other differences.
One last thing: why are elves granted things such as +2 Str, -2 (whatever) for being wild when similar human tribes are not? We do not see human sub-races for woodland humans, jungle humans, desert humans, wild / savage humans, etc. In fact, I think some people would take offense if such sub-races of humans were suggested, as we do not notice consistent and major differences in the RW between humans raised in a desert tribe and those raised in a major modern city - or in the forested mountains, etc. So why should we see the same for elves? That has been my main quibble with the whole 'multitude of sub-races for every possible environment' situation.