There are some high karma accounts which make a great contribution, and others which ... don't. I'm doubtful whether karma or account age has a significant signal beyond anti-spam.

But it would be useful to know if I had up/down voted them significantly in the past.

The only thing karma reliably indicates is participation over time, the signal is too noisy for anything else. If anything high karma should be a red flag. The very best contributors here rarely comment because they have better things to do. It shows an 8/8 score for me and I doubt anyone would consider me a top tier high quality contributor.

A plugin like HN Comments Owl would be more useful IMHO.