For those of you that need justification with "higher authorities" for the price of adding a tower, here's some that worked for me!
"We can get all the crap off the floor of the boat, you'll stop stubbing your toes on wakeboards" (don't mention that you need 600$ worth of racks quite yet)
"We can get a bigger, higher bimini so you'll stop smacking your head (or mall chick hair) on the winshield mounted one" (once again, refrain from mentioning the $600 for a new bimini)
"It keeps the rope above the heads of the people sitting in the back seat. You can't sit in the back of a DD with the rope on the ski pylon while riding."
"Chicks dig boats with towers!"
DON'T use that last one, unless you have an adventurous person in your life...