I've had the VQ 3000 for about six years and I find I have to clean frequently and thoroughly to have the bobbin sensor work. I've never had the sensor replaced.
In fact, other than routine servicing, the only thing I've had go bad in the six years is the electronic needle threader, which was replaced three years ago for about $12. The newer one just died, and unfortunately I'm going to have to drive about 90 minutes to the dealer here (we moved since I bought the machine.) There are videos online on how to do it, and I know it's only a five minute job, but I'd rather have someone who knows what they're doing replace it for me.
Other than that the VQ3000 Dreamweaver has been great!