Fix up old road bike or buy new one?
If you are coming back from a long layoff, I'd fix the Cannondale, then if you keep up riding in the future, spend some time considering if you want to upgrade and what to. It's never a good idea to be choosing a new bike under pressure to get riding. 

Make sure the things the repair shop wants to replace are really needed. Cables and housings - yes that's a good idea and relatively inexpensive, but you could do that yourself. 

Chain and cassette - make the shop prove they are worn out to the point of needing replacement. If not ride them until the do.

Definitely get the shop to explain why exactly they want to replace the wheels, and what they want to replace them with. You might be able to get a better deal on the used market through Craigslist or Ebay.