Whats the general consensus on the state of cleanliness of mountain bikes, particularly among professional riders in the MTB discipline - do they truly prioritize and understand the importance of a meticulously maintained and clean bike, or is it often overlooked in favor of other aspects of their training and preparation? Is the dusty, worn-out appearance of many MTB bikes a badge of honor, signifying a riders toughness and ability to endure harsh conditions, or is it simply a reflection of a lack of attention to detail? Do riders genuinely believe that a clean bike is a faster bike, or is the relationship between cleanliness and performance not as clear-cut as it is in other cycling disciplines? Are there any notable exceptions or examples of MTB riders who are known for their meticulous bike maintenance and presentation, and what can be learned from their approach?