LTE is part of Network Vision, but it's the long-term part. Like Wimax, LTE requires a completely separate network infrastructure on different freqencies than CDMA and is hugely expensive to implement; AT&T and Verizon are spending upwards of a billon dollars per major metro market on their LTE deployments. Sprint doesn't have that kind of coin so plans to build out LTE in conjunction with partners Clearwire and Lightsquared, both of which have had various technical and/or financial problems. Long story short, it will take Sprint years to build out LTE.
Network Vision is about taking the iDEN (800MHz), CDMA (1.9GHz), and WiMax (2.5GHz) towers and combining them into a single multi-mode tower with new backaul and radios. Clear claims LTE is mostly a software upgrade for them. If Sprint was planning on including WiMax (2.5GHz) on their multi-mode towers, I can't believe the *incremental* costs of LTE are that much more, especially considering Clear is saying LTE is mostly a software upgrade for their WiMax infrastructure.
The "hugely expensive" part for Sprint is Network Vision itself and is equivalent to the billions Verizon and ATT are spending. Then you have Evdo Rev B being mostly a software upgrade for the CDMA modules and LTE being mostly a software upgrade for WiMax modules (or dropping WiMax and just deploying LTE instead)
Given how much tearing apart they are doing, I would find it difficult to believe they aren't seriously considering deploying LTE at the same time. They were already planning on deploying WiMax on their towers as part of Network Vision and Sprint has acknowledged LTE is in their future. I think the consideration isn't about billions of dollars to roll out LTE, but rather whether they should take the money allocated to deploying WiMax on their multi-mode towers and redirecting that to LTE.
You can see the type of changes Sprint is saying they are doing for network vision in the picture they provide:
Sprint Newsroom | Sprint Network Vision Information Center