They're imho one of the most important races in WoW and have since WC2 been a staple of the Alliance's general appearance and story. I wouldn't care if they were just Blood Elves with blue eyes as I just don't see that as something that will really hold them back.
I also don't believe the numbers game is that detrimental to this question. Other races in WoW are rare but that hasn't stopped them from playing major roles in the story such as the Blue Dragonflight or even the Darkspear Trolls which have always been a single small Tribe that faced many threats upon it's introduction to the Horde which have otherwise reduced their population in a large way Kul Tiras attacking on their home island, Kul Tiras attacking again, Zalazane and now Garrosh attempt to cull them.
They are rare. But I feel this can only add to the experience. Playing a dwindling race is always great as it definitely adds a unique aesthetic to them. It would also keep the embers hot on Blood Elf lore. We've also always seen the odd High Elf dotted around an Alliance base so with the addition of them being playable I don't think it would change much.