Headphone out sure is handy but I've tried countless "headphone out" and headphone combinations and none gave me a comfortable feeling. It always felt the amp was trying to get as close to my eardrums as possible.
I never expected it to but the vox amplug 2 (metal) has just enough features and gives me a chill yet very saturated sound (yes, even some reverb). Since I have the little critter, I don't even bother checking headphone out capabilities.
As it comes to speaker out capabilities; that makes your rig scaleable and it's always fun to experiment with that. even though results wont be optimal, running a 5w amp to a set of 12" speakers, it gives you some options. Imagine upscaling your amp with a small extra cabinet with a different character. An option to either cut the sound of the speaker in your combo or leave it on to have 2 speakers with different flavour seems like a fun upscaling.
anyway, it wouldn't stop me to experiment with it; as long as your amp isn't too powerful for your speakers and the ohm values don't mess up your gear...why not.