The h-vac guy generally supports the idea of a central air conditioning rather than the use of multiple window units. It's a cost factor and it makes sense to cool the entire house rather than just sections of your home.
Installing a new split system may actually save you money. If your using window units to cool your home, you can save money by installing modern 13 Seer split system. Wouldn't you say that it cost $25 p/month to run one 18,000 BTU window air conditioner, plus you lose the window and you have to install it every spring!
OWN THE BOOK THAT TELLS YOU HOW TO ENJOY YOUR HOUSE MORE