Can an upper blepharoplasty cause eyebrows to drop? (Photos)

A blepharoplasty will not lower your eyebrows.  Your eyebrow position is fine and should not change should you pursue an upper lid bleph.  It would be a nice procedure for you. 

From the photos you posted it appears your brows are in satisfactory position and are not exhibiting ptosis (drooping of the brows).  In patients that exhibit ptosis, as well as upper eyelid aging, a browlift should be performed in conjunction with upper blepharoplasty to prevent further eyebrow descent.  In your case, an upper blepharoplasty alone would be an excellent procedure to rejuvenate and refresh the tired appearance of the upper lids.  I suggest you be evaluated by a surgeon specializing in facial cosmetic surgery to research your options.  Good Luck!