The ion cx is a nice bike. I nearly bought one myself. I went with a custom built cross check instead as I did t want the cross crank that comes on the ion and I wanted a front rack that the ion can't do.
The ion does have mounts for a rear rack, and I am not sure about fenders...if that's even important to you.
Yes 38 tires are significantly wider then 25
I think you need to ride it, as the geometry is going to be different than your current bike.
If you can actually find one a specialized tri cross may meet your needs as well...they have a disc model with apex on it, I believe.