Rick,
As far as the belt sander goes, there's only one thing against it and that is the fact is is a 'belt sander'. Our experience of 35 years indicates to us that a 12" disk sander will do anything that a belt type will do with far fewer problems, much easier set-up, and a quality 12" Disk Sander similar to the Jet we bought 8 years ago WILL NOT 'Snipe" your boards during thickness sanding like a belt type will. We had a delta combo belt and disk for 24 years and after just a year we were only using the Disk half of that machine. With just a few jigs you can easily make from scrap hardwood, you can precisely square wood or metal and thickness sand 20 foot long pieces of wood to within a few thousanths of an inch again and again. For metal, there is absolutely no comparison! The disk wins hands down. Other than our bandsaw, it is the second most used tool in our shop.
Hope this info helps you,
Tracy