If they were gentiles, they never kept the Jewish holy days. How could they then turn back to them? Besides, like I said before, the greek words used are consistently used to denote civil times and days, NOT jewish times and days which are referred to by different words.
The Galatians, feeling betrayed by Paul, write him a letter. They wanted to keep the Law of Moses. The letter back to the Galatians are why the Law of Moses had been set aside.
My point is what the beggerly things they wanted to turn back to was the Law -- with its forms, and symbols, and days... The verses you used has to be kept with the Chapter Three. To break them out and suddenly have Paul start talking about "pagan holidays" doesn't fit Paul's flow. They, the Galatians, wanted to keep all of it... Paul says don't turn back to that...