Recently there haven't been any bonuses that will increase your milage. The transfer bonuses frequently allow you to BUY more miles at 1.1 CPM. If your trying to sell your miles, I would think the price is lower when you can buy them from DL themselves at 1.1. (The only reason the miles would be worth more is if someone doesn't have an acct with miles in it to start transferring, but thats not very likely to happen IMHO.)
If you'd like to book a flight, but need more miles, definitely pays to pay until you can buy the additional miles at 1.1.