I just moved my 15G to a 29G last month with no problems. I decided to use a sand bed instead of crushed coral this time so I started by soaking the sand in the new tank with about 5 gallons of fresh saltwater over night. After the fines had settled I just moved everything over form my old tank then added as much of the old water to the new tank as I could get out. Then topped off with fresh saltwater, about another 7 gallons. Also added some stove warmed seawater to raise temp back up as I didn't preheat my fresh saltwater. All the corals opened right back up and I've lost nothing. Also got new T5's to replace my PC's which look fantastic.
Probably should add that I wouldn't recommend using old substrate, get new stuff, because of all the decayed matter which could lead to H2S issue in new tank. And have plenty of premade saltwater handy. I had 14 gallons made up in advance for the move, I used 7 gallon water jugs I bought at wal-Mart for $8 each.