That should work...you're just slaving amp 2 off amp 1's preamp. It sounding good may be the problem...you're adding a lot of variables in the signal chain, amp 1's preamp may sound bad into amp 2's power section, the quality of the sends on the effects pedal, etc.. should't hurt anything to try it though.
On a related (but different) note...I've been looking at one of these...

The ability to re-amp the spk output of my tweed deluxe and have a 100 watts on-tap would make for a killer/scalable rig. Set the deluxe volume at it's sweet spot then push it back through the speaker at what ever volume you need to cover the room. That's awesome! Plus you can put effects in-between the 2 power sections. It's pricey though.