Yichus is a great indicator, insofar as you are looking for the right thing. As nolongersingle points out, ehrliche grandparents is wonderful yichus (if you are looking for an ehrliche spouse).
The problem with that point is that it is meaningless. When people say they want yichus, they mean “IMPORTANT” yichus. Importance is not indicative of anything and I would argue that there is zero correlation between IMPORTANCE yichus and anything other than self-importance.*
*This is not to say that people with important yichus are self important. It is just to say there might be a tiny correlation because some people might use yichus to expand their self-importance.