humidty problems in a house are not because of a tight house or because of poly. Both of these a good things! the tighter the house, the better, for a number of reasons. The problem arises when there is inadequate or non-existent measure to control indoor air quality. What do you have for an air mangement system? You may consider an air-to-air exchange, or even a cenral exhaust fan connected to a dehumidistat in conjunction with allowing for make-up air works well (It's what I did on my house, & I have one of the tightest houses you will find).
As regards your crawlspace, if you are experiencing winter condensation, a central ventilation system should solve this too. If your experiencing summer condensation, getting rid of the crawlspace vents will help (Letting hot,humid summer air into a cool crawlspace will case condesation. The only time a crawlspace should be vented is when the floor is insulated and the crawlspace is outside of the thermal envelope. Then the vents should be open in the winter & shut in the summer, contrary to common prcedures. This is NOT a method I recommend. You are better off keeping the crawlspace in the thermal envelope, even insulating the foundation perimeter.)