What is really necessary?
Fresh air, some water, a snack and a lekker trail on your preferred bike. Sorted.
For me, I enjoy events and compete against myself. Aside from the training effect over the years (and gained experiences, knowledge etc.), the reduction in bike weight (and some personal weight) has had a definite increase in positive "output".
Without a doubt you will be faster on a lighter bike (assuming skill level remains at was constant). One needs to also bear in mind, that you need to find a bike that "suits" you best in terms of geometry, set-up, general specs etc.) for the type of riding you do. Not all bikes are equal, even with the same weight.
The question you pose is but a highly personal one. What is the cost value you are prepared to "endure" to achieve your own personal happy medium.
