I've been testing cameras side-by-side, 5 vs. 5s. I am a photographer (for fun, not for pay!)- the one thing I do *daily* (beyond standard iPhone stuff) is take photos. More often than not, they are low light: at dawn, at dusk...etc. The difference is (believe it or not) feels worth the big spend for me. Also, the space gray is gorgeous in its sleek-yet-not-total-blackness.
Thanks to Apple's amazing customer service, I have 30 days to decide (I mostly already decided). I'll sell the 5 still on AppleCare- and use next upgrade for next round. My carrier thoughtfully replaced a bum 5 in Feb (which was great) - yet also thoughtfully extended my contract until Feb 2015 (vs Sep 2014), which was not so great. At the time, after a week w/ no working phone, I was glad to have new-out-of-retail box (no a service replacement), and willing to take the black they had vs the white they couldn't get to work properly.
This will keep me till then. Another 1-2 years could see some interesting developments in carrier and/ or contract options, so I'll just wait and see. In two years, the tech world could change - yet in two years or ten, space gray will still be a timeless beauty.