It's not only the re-stock fee. If you decide you dislike the replacement (in your case wanting the DX), you are stuck with the 2nd phone (the Fasc) no matter what. They won't allow you to pay another re-stock fee and get a 3rd phone.
IDK how you're going to go from the Bold to the Fascinate to the X. Unless something is terribly wrong with your Fasc, you're stuck with it. I had tried that a while back when I got an upgrade, exchanged it for some LG phone, paid the $35 fee and really didn't like it, tried to exchange for 3rd phone but was told I was stuck with it and there was nothing I could do.
Return Policy - Verizon Wireless