The Spyders aren't all that bad, at least not from 3 on. I started out with Spyders 2 and 3 and moved on to the i1 D3 when it came out (yes, it is better).
The main problem with the Spyders, IME, isn't overall color balance, which has generally been good, but hitting the precise position of the primaries. This affects how certain saturated colors are displayed.
It should also be said that I still have an Eizo-branded Spyder3, which I have tested against the i1 D3 in both Eizo ColorNavigator and NEC Spectraview II, and they are completely indistinguishable. This suggests that if they could get their manufacturing tolerances tightened up, they might have a product that could compete (and improve their reputation).
What I see as the main advantages of the i1, are the dichroic glass filters that won't fade, and also the long light path/lens system, which should minimize the risk of "IPS white glow" affecting the black measurement.