I use a combination of Voxengo SPAN/AnSpec and T-Racks Metering, and while it works just fine, it would be nice if SONAR has its own dockable metering suite as has been suggested. More streamlined than having a handful of plugin windows open.
As Soundwise has already brought up, SONAR
already has spectrum analyzer functionality (Quad-Curve EQ), standard track meters, etc. so I wouldn't think it would be a major undertaking to create a suite like this. Then again, I've developed software as often as I've walked on the moon, so what do I know!