This may be one of those cases where the "first reader" principle needs to be applied. By this I mean that what was written may have had more significance to those to whom it was originally written, the first readers, than it does to us. The principle expressed in the text has application for all time, though the specific issue may not.
By way of example, consider Paul's instructions to those who had the gift of tongues in Corinth (1 Cor 14). The main principle in this passage IMO is this:
1Co 14:26 How is it then, brethren? when ye come together, every one of you hath a psalm, hath a doctrine, hath a tongue, hath a revelation, hath an interpretation. Let all things be done unto edifying.
1Co 14:40 Let all things be done decently and in order.
The issue at the time was the use (or misuse) of miraculous spiritual gifts. Those have long since past, (though some may argue to the contrary, as is their right), so the specific issue is not something we have to deal with today.
The overlying principle, that of orderly edification, still applies.
The first readers of Rom 14 had lifetimes of Jewish ceremony and culture to work through. Again, these things had in the past been authorized by God. They had believed and obeyed the gospel, and were no longer Jews in a religious sense, having become Christians. Nationally, they were still Jews, and different nations have different customs and observances.
For them to forsake so many things that were peculiarly Jewish would have put them at odds with friends and family, even more so than recognizing Jesus as the long-awaited Messiah. Once again, the Jewish feasts, etc had at one time been sanctioned by Jehovah, and their purpose was to bring to remembrance national events and to point to the Messiah. There would be no sin in continuing to remember these things.
Seeking justification through their observance would be a problem, though, thus the warnings against such elsewhere.
The Galatian Gentiles had not been Jews, would not be recalling Jewish national events, and did not need to take on any "Jewish characteristics" at all. Their former religious rites had never been authorized by God, and often consisted of wickedness, anyway, so for them to either seek justification in the Law, or to return to their former ways would have been sin.
They were complete in Christ, as any and all can be today. There is no need nor logic in seeking authority for religion in the OT when the NT is far superior, and far simpler. Though many OT principles still apply, men today are not under that covenant.