Is it worth it? That's something only you can answer. Myself, I prefer to leave the manual windows in place because the car is a classic and I like the overall appearance and functionality to remain that way.
About the only changes that I will make to my car are safety or modifications that aren't real extreme; wheels, carb, exhaust, cam, that sort of thing.
It's all about what you want with your car.
1967 Mustang GT Convertible: Edelbrock Headers and Carb, Strut Tower Brace, Front Disc Brakes, Everything else ORIGINAL
2006 Infiniti G35 Coupe: NISMO CAI, NISMO Braided Clutch Line, Tein Hood Dampers, NRG CF Engine Cover, Vortec SC comming soon