I spend more where it actually matters to spend more. With instruments, there will always be differences among entry-level, mid-level, and pro-level so I tend to spend more on these; where it might matter and will give you a real-world (meaning usable) advantage. I find this to be true also with products such as cars (say, choosing between a Chery and a Honda), audio equipment (Minami or Kenwood), video equipment (Asahi or Sony), etc.
However, with bags, belts, and shoes, I don't spend more on designer brands of these products. I can't seem to rationalize spending Php50K on a bag because a Php500 bag will actually serve the same purpose (its SOLE purpose actually) of carrying my stuff around. Designer brands may be chic but, for me, they don't offer any "special" advantage that could justify their steep price.
And this has something to do with these products' designs. Belts, bags, and shoes aren't that complicated at all in their design. So, in the simplicity of their design, I find they could only offer two real-world advantages over their cheaper counterparts: AESTHETICS & STURDINESS. Meanwhile, with a product as complicated as a car, or an amplifier, or an LCD TV, aside from the two aforementioned advantages they may have technology incorporated in their design that may actually give you a lot more usable advantages. Thus, it may be wise to spend more on these types of products.
But if LV could come up with a pair of shoes that could pick up women (yung tipong may push button sa sole and, when pressed, the woman you are talking with will become instantly attracted to you), I might pay 50K for those. Until then, a 50K-pair-o'-shoes will, at the end of the day, still just be a pair of shoes.