Better a limited growth than no growth at all due to the total failure of the airdrop - which is the current status with the sms verification only. As Zach said KYC is also a bad idea, but adding a proof of bitcointalk account (add a field with bitcointalk account in x-cash profile and make a proof of account post on a dedicated thread of bitcointalk - not the main ANN thread please, or otherwise adding Xcash address to Bitcointalk profile as suggested) would surely improve the situation, of course keeping the SMS verification as well. Of course you would have to limit the quantity of eligible bitcointalk accounts - either by time (only accounts created before the xx day/month/year are eligible) and/or rank (starting from Jr Member or even better Member) and exclusion of red trusted accounts. You may even put as a requitement the need of having a few "earned" merits - this would give another cut on multiaccounters. You will have anyway some multiaccounters also with bitcointalk verification but surely not as much as with just sms. Moreover, people skilled in cheating with bitcointalk may not be skilled in cheating with sms and viceversa - and you'd need to excel in both skills to be able to abuse the system.
On the other side if you keep the current sms only criteria you may as well abort the project since you'd be critically harming it: legit airdrop receivers would leave an airdrop worth a couple of cents (not worth their time) while billions of coins would end up in the bags of professional scammers, who by the way seem to clever enough not to dump their coins on exchanges - for the moment.
My two cents.