I think the spring FCS playoff has a much higher profile this year than normal due to the spring timing. They are not competing with the bowl games. The early round FCS games normally don't even get on cable except for ESPN3. I think the semi-finals might normally get on cable, but I am not sure. This year several of the early round games were on ESPN or ESPN2, including three of the four last weekend. I watched those three (plus JMU/VMI), and I'd bet they all had really good ratings. Normally, the championship game is viewed about as much as a lower-level bowl game, so it is sort of wash as to whether or not JMU is better off in FCS for now, but this year, FCS is probably better.
The FCS regular season seemed to get ignored this year, but the playoffs have been great.
Also, picking ODU is not really a good example. Coastal Carolina and Liberty are very happy with their choice. I suspect JMU in the Sun Belt would be awesome for their fans.