My experience with the Salsa - they are wickedly good young and fresh. After about a year they get flat and stay there until 3 years+ old and then exit with the same rich spicy flavor but much smoother. If your box is 3 years it should be prime smoking. I would have no fear aging them 3 more years though. I am suprised you have held onto a whole box of Salsas soo long - great will power you have!
I have a theory that the more complex the blend of a cigar is the longer it spends in its sick period. Since the Salsa has a 3 nation blend I put several sticks down for a long rest when I noticed they had dulled and didn't visit them for a couple years and then they were awesome again.. (and gone all too quickly)
3 year old Buc Z's are quite nice too!