Harry, I think it all depends on where your pre-calibration starting point is. You seem to have been lucky and had a monitor that was very close to "true" to begin with. Unless you get a hardware based calibrator, you would never know this. Also, it may be worth checking a range of different images that contain different balances of colours. The one(s) you have checked so far may show little difference, but other images with different colours may show a greater difference.
I found little difference in blues and greens with my CRT, but the reds were noticeably improved. Your monitor may have a different amount of before/after correction applied to different colours. The biggest improvement has been to my LCD screen. The colours aren't that different, but the black/white and greys are much improved. So, you may find that the colour balance may not be that much changed, but there's differences in the mid tone details.
If you haven't seen an improvement then you have a point that you may have wasted your money. Without wasting your money, you'd have probably never known this!
Duncan
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