The buy and gift offers aren’t terribly attractive at 2.8 cents per mile, plus a 7.5% tax. In other words you can buy or gift 30,000 miles and receive 52,500 miles for $840+$63 tax=$903. That lowers the effective price per mile to 1.72 cents. While it may be worth buying Continental or AAmerican miles at that rate I don’t think Delta’s Skypesos are worth nearly that much.
However if you have a couple family members with 30,000 miles in their account it may make sense to transfer with this promo to consolidate the miles into one account to book an international ticket. The cost to transfer 30,000 miles is $330 with fees and the recipient will receive 52,500 miles with the bonus. In other words the additional 22,500 miles cost 1.467 cents per mile, plus you were able to consolidate the other 30,000 miles into a bigger account where they may get better use.
People have had good luck with redemptions on V Australia using Delta miles. A business class flight to Sydney on V Australia would run 150,000 Delta miles.
HT: Israel J.