We were also not allowed to sit around without shoes when I was growing up because it was considered a sign of aveilus. If we wanted to take off our shoes, we had to put on slippers.
I think Shabbos shoes are important, as long as one can afford them.
I think a Shabbos or YomTov table should look good, so I don’t think using cheap disposable dishes or flatware is OK, but there are very nice things in the market that make the table Shabbos’dig or YomTov’dig, yet can be thrown out after the s’udah.