@Nole Lou what do you think?
I neither believe in dressing like trash for church, nor getting extremely dressed up.
The way I used to think about it, and I think appropriately, is something equivalent to work attire, in the range of business casual to shirt and tie. Of course, the idea of work attire is kind of out the window now too.
To me, you should be paying the minimal respect to the act of mass to get dressed in something other than what you were lounging around in or gardening in. It's to get in the right mindset, and if you are a believing Catholic going to Catholic mass, you are in the actual presence of Christ. It's not a matter of "Mmm, shorts are not good enough for Jesus" it's more like "Mmm, Jesus is not worthy of me going upstairs and putting on socks." Putting a certain minimum level of care and effort into it helps remind you that you are there for a reason, and its important.
There's no "minimum acceptable" because everyone's circumstances are different, but I know damn well that the people where I go to church are not choosing between flip flops and barefoot.
That said, dressing way beyond the norm of what you normally would wear for work or a nice dinner out, for showing off "Sunday best", that isn't appropriate to me either. You're not their to put on a show.