From where I sit, the answer is clearly "yes", but I think it's probably the wrong question. Better to ask if parents can be too involved in helping their kids have school success, and then I think the answer is: "Not if that involvement is done right".
Rare is the school that has to turn away parent volunteers and where teachers wished parents would be less connected. And parent involvement done right includes just the kind of balance and systematic loosening of the reins that Lisa is looking for. Moreover, involvement is a lot more than attending meetings and school events (though I love those for their involvement benefits and their community-building elements); involvement also includes appropriate partnering on homework and school progress and making sure your child has the support he or she needs to flourish in his or her own way.