I always take Amtrak to WDW (have been for the past 12 years or more). I view my train travel as part of my vacation--not as just a mode of transportation. I travel alone usually and reserve the standard sleeper, which for me is just fine. I sit back, read, relax. I don't have to worry about de-icing or traffic jams.
Yes, a sleeper is usually more expensive than flying, but there are fewer hassles with a train. JMHO
In the past, we have taken our children to WDW in coach. The kids loved it. I think it was a great experience for them.
I don't think train travel is for everyone. If someone is in a hurry to get somewhere, then this probably would not be an option. Also if a person is the type who just can't sit and relax for an extended period (like my DH), then a plane may be better for them. But I prefer to take things easy. No long security lines, no fretting over the weather. I arrive at WDW relaxed and rested--a good way to begin a vacation.