Oh I think it's worth it. Here's what I'd do. Pull your plugs and have a look first. Black and sooty? Sooty black smoke from the tail pipe? My guess is that your Rochester is running filthy rich. That and your timing might be severely retarded. Once you resolve those, I think you should come up to at least 15 mpg.
And yes, I'd say the $140-ish expense to swap to the Holley/Webber carb was well worth it. Also, the $74 swap to a Pertronix electronic ignition conversion on the distributor was worth it too. Shoot, with $4+ a gallon gas, spending a few hundred bucks to modernize just a little bit and pick up 6 mpg should pay itself off pretty quickly.
