So you are using the camera, in effect, as the analogue to digital converter. I assume that is via firewire from the camera and capturing in a DV codec ?
This should certainly be up to capturing the original VHS quality without loss.
I think some models have a TBC inbuilt that can help, you would have to check out which.
You would still be using the same VTR for playback substituting the Canopus for the camera. I am not sure it would make a massive difference to the quality of your digital capture but its possible the Canopus has slightly better circuitry than your camera. VHS is inherently noisy and grainy so are you saying that the digital files are much worse than the original VHS ?
Short of just buying the Canopus and trying it I am not sure how you can really test though.
If your captured footage matches the VHS then there is not much you can do to improve it in capture. As Shane says a model with a TBC might smooth out some of the "lumps and bumps" but you are not really going to get that much better.
What you might want to consider though is a plug-in called Neat Video. It is a fantastic de-noiser and will possibly improve your VHS footage quite a bit.
I think there is a free demo. Give it a go. Its going to cost you less than a Canopus but you will be in for some long renders if you have many hours of footage.
The only thing you can do to improve the capture (not the picture) is to use a good IO card and capturing in Prores.
The footage won't be better than on the original tape, but you will avoid adding further compression (DV).