my friend has the 50W and it's a good amp for home use, not loud enough for a band situation unless you have it mic'd up but your main concern seems to be the effects loop.

I don't think you will truely benefit from having one, the main purpose would be for modulation effects and can also be a benefit for a looper but only if you wanted you looper to completely bypass the onboard effects. 

As you seem to be leaning towards a katana to eliminate effects pedals and use the onboard effects i wouldn't pay the extra for the louder volume and effects loop myself but just so i'm clear you mentioned earlier you think you could buy a pedal that would give you this feature, you can't. The effects loop connects to the amplifier circuit after the pre-amp and you can not achieve this without hard wiring.