While there is little doubt that tapered square spindles are now used on lower end cranks, there is nothing inherently crappy about them — my old mountain bike has XTR components (1993 vintage) with square tapered spindles, and, after almost 20 years of hard use, there is really nothing wrong with the crank, and I have seen no reason to change it.
Really, a higher-end crank is not likely to make you any faster, unlike, say, a better fork, lighter wheels etc.