A place for everybody
The closest thing that I have ever seen to Jesus speaking on something as relating to denomonations is found in Mark 9:38-40 / Luke 9:49-50. Mark's account follows.
38 And John answered him, saying, Master, we saw one casting out devils in thy name, and he followeth not us: and we forbad him, because he followeth not us. 39 But Jesus said, Forbid him not: for there is no man which shall do a miracle in my name, that can lightly speak evil of me. 40 For he that is not against us is on our part.
If someone knows of other references, please share them.
Now, as for attire...please note that there are an awful lot of scriptures relating to attire both in the OT and NT. Read them for yourselves...pray...and let the Lord speak to you.
We must understand that there is a different requirement for those who serve the congregation (preachers, teachers, ushers, choir members, secretaries, custodians, parking attendants, etc.) than for those who are IN the congregation. Those IN the congregation can feel free to "come as you are" to a certain extent. However, those who are ministering have roles beyond merely being participants in the worship experience. These people are the leaders...whether you are preaching the Word, wielding a mop, or singing in the choir. The congregants take their queues from the leaders. God has ordained it that way because he is the God of ORDER. Congregations generally take on the personality of the senior leader.
Let me stick to the choir since that is easiest. Choirs who wear robes do so for one basic purpose: A visual display of unity - emulating God Himself. It is a uniform...and a uniform means exactly what the term implies - everybody looking as much the same as possible. It is a military concept that goes back to Joshua at Jericho and to Jehoshaphat and Judah. The Levites (those who served in the worship) had uniforms. Jesus wore clothes that spoke of his rabbinical engagement. It makes it easy for those who may not be familiar with who you are to know what you do...and that creates opportunities for you to minister. What I am simply trying to say is that attire and decorum have their place in church. It works well for some people and turns others off. We will simply have to deal with that. As it relates to numbers in the congregation...having large numbers has never constituted the approval of God. Most often God tends to the smaller number. That said, if a person doesn't fit in a congregation that embraces those formal/semi-formal trappings and they can find a congregation that is less formal but serves good food and good teaching, then help them out the door in a hurry. If that causes them to grow more rapidly "over yonder", then let's help that part of the body to develop. There is nothing wrong with either position.
I will tell you that when ministering on the street, in tents, or parking lots I run into street walkers (both male and female) who dress the part. I don't begrudge their appearance because they are involved in what they are doing and I am their to offer Christ. However, I am offended when I make an altar call at a church and members who are not street walkers come to the altar dressed as though they are street walkers. You cannot clean fish before you catch them, but once you do catch them you had better get to work on them pretty quickly. If you don't, then they, you, and your whole environment will start to carry and odor that you won't rid yourself of easily.
Finally, denomonations don't bother me at all. Like I said, I cannot find a lot of scripture against them. What bothers me is the segregation in the church - and there IS plenty of scripture against that.