How thick should the front baffle of speakers be?

3/4 inch plywood as used in vintage Altec's and JBL's will work just fine!

plywood works. I question the use of large drivers 10" and above that can shake the wood. I also question the method of attaching drivers to the face of a cabinet. Where is the technology? I feel let down. 

The 3/4" plywood used in the vintage JBLs probably did vibrate, but in a way that was pleasant to the ear.  For me, I am not particularly partial to speakers with heavy cabinets, but that's probably more to do with the overall design than the cabinet per-se.  

@soundsrealaudio- Martinis should be stirred, not shaken.  Just sayin' ;-)

Well, I suppose someone should tell Alon Wolf he's got it all wrong.. :-)