Just remember that PureDisk can dedup with regular storage disks not on your VTL. SO if you are paying a TON more for a VTL than just storage for netapps deduplication, you may want to consider just buying the puredisk licensing instead which will probabbly save you quite a bit. Also, if they have exchange, and you want to do granular restore (this is VERY nice for any exchange admin) then you'll want disk storage as that is currently the only way for performing granular restore.
Since people are moving to disk storage as the future, at least for development (take for example, synthetic backups perform better on a disk storage than a "tape mount" from a VTL), you may want to consider being in that range.
However, If netapp is offering something amazing on its VTL that is a "Must Have" then you may want to consider that.... i know for example that alot of the SAN configuration is easier to do with the VTL in my past experience).