Auh,
I searched for the significance of kudumi and found this one:
http://www.tamilbrahmins.com/showthread.php?t=4402
We TBs are very shallow in our search for roots of our cultural practices and are satisfied with some internet link, whether authentic or inauthentic. This is one of the main problems when we are required to defend the practice or giving up of the practice.
There is no direct mandate of maintaining Shikha in vedas per se. But inferences abound.
A brAhmaNan is referred to as "AgnEya" in ShathapAtha BrAhmanam of Sukla Yajurveda in the vedic mantra "AgnEyO vai brAhmaNah:" and postulating this smruti says "agni chiHnam Shikha karma" meaning Shikha is symbolic representation by a brAhmaNan of agni.
It logically proceeds that without shikha a brAhmaNan is ineligible to perform any "agni kAryam" including simple homan and even pitr ShrAddham.
That is why we find sanyAsi dispensing with upavItam, Shikha etc. when they take up sanyAsa Ashrama giving up all karmAs including agni karmAs.
Even leaving aside all the agni kAryams etc. many of the TBs religiously chant at least one sahasra nAmam, the most popular being Sri Vishnu SahasranAmam. Before japa viniyOga of a sahasranAmam, anga-nyAsa and kara-nyAsa are mandated where "Shikha" is one of the places touched for invoking a particular devata (or an avatara of devata) at Shikha.
If we are doing the said anga-nyAsa without having the shikhA, we are probably doing an empty ritual without maintaining the shikhA.
In addition to shikhA, a brahmin has to wear an upavItam, wear pancha-kachcham, shikhA should be tied (baddhAshikhO), should be a dhIraH (one with controlled senses) and should be a krutAhnikaH (a performer of prescribed Ahnikhams like sandhya vandanam etc).
The rigors of life are tough indeed for a brAhmaNan and it is not as easy as giving up "shikha" just because others have given it up.