Simple living means that you incur expenditure on necessaries and comforts or even on luxury but not for influencing others with your life style. Even over simplicity for influencing others is not simplicity. simplicity consists of adopting a life style suitable to your environment without inviting undue attention of others.
Spiritual living is meaningless term. Living may be simple, moderate or luxurious. This is always physical. Possibly, interaction with others and socialization may also constitute life style. But this is also not spiritual.
Simple living is living normally by avoiding unnecessary things but have a lot of wishes.
But,Living spiritually is living an ordinary life without any wishes.
When I see monks of a particular famous religious order to be travelling in Mercedez with pilot cars the diffference between the two becomes so poignantly clear!
Life may be simple, moderate or luxurious. 'Spirtual life' is meaningless term. As long as you are a human body with brain, blood and bones, you have only physical living- simple, moderate or luxurious.
What is 'spiritual living'. Is this how a 'soul' without physical body lives. Then only ghosts, evil or good spirits live spiritually. Thus 'spiritual life' refers to ghosts.
A spiritual life could as spiritual as one can make out of it! It's something that can at best produce a stormy and futile debate without any definitive outcome. It's best left to the individuals concerned!
Simple living is like living simply without any luxuries while spiritual living means living realizing your true inner self. I think simple living is related with spiritual living...