I would just tell them that the current crop of bikes is great and to pick up a biker mag (rider or whatever) and give it a read.
This gives them something they CAN do and might plant the seed of an idea. Maybe that seed grows into a pair?
My wife knows I ride and i pretty much do what I want as long as it is planned out and doesnt conflict with something she already planned. We have separate finances so her Juut salon and Starbucks habit doesn't pinch into my Ducati and bicycle habit.
I don't bitch at her for spending $180 at the salon and she doesn't ask how much I spend at the Duc shop :-)
We do have a kid and we both have big insurance policies. Because I ride and mtn bike and generally could get myself killed and her because her family history is all heart disease and cancer. She is good looking, but the next guy might not like my kid being in the picture. Me, I'm decent enough looking but my tolerance for other people is very low, so my dating success would be limited to sluts and no real relationship, so ill need that insurance ;-)