I think not unless you have enormous power. Also i believe the codex in Cineform is better than the Vegas version (this may have changed in 8). I don't think intermediaries will be out until we have Vegas 64 bit and very fast 64 bit machines and super fast scsi hdds.
For HDV and one or two render generations - you can edit in m2t. For AVCHD, you will still need Cineform. Just one example - depends on your hardware power too.