Hold Metal Windows vs. New Vynal in a ReHab?

[Jon Elson]

I am rehabbing a house built in 1959. Margins are tight. The house has old metal windows that close left to right (vs. standard up and down). The house probably has a dozen windows like this as well as a massive picture window in the living room. If the wood floors, bathrooms, kitchen, and hardware are redone, will leaving the windows decrease the value immensely? Is there a way to clean up the windows so they look nice? They function fine. Any ideas and opinions would be great!