I am trying to decide whether to upgrade a 914-6 with a 2.7rs engine to something much hotter, perhaps a 3.2 or 3.6 built.

Do you think this would make a huge difference for a car only driven on the street?

What other upgrades do I need to make?

How costly would this be?

I value the torque pulling out of corners.

Is the 2.7 MFI, carbs? The 3.2, 3.6 carbs or Motronic?

The injection system will definitely make a difference in the drivability. A built 3.6 or 3.8 could be scary fast in a 914. I personally think a hot 2.7RS setup with the right cams, injection, headers, etc...is a good balance for our little cars with 210 hp or so.

if you're interested in selling your 2,7RS, email or PM with details.
i'm not in a panick hurry but i do see this in my future...
the geography is a plus ...

Engine has dual webers. Is mechanical fuel injection a worthwhile upgrade?

you hafta define "worthwhile" ...
it was worth 15HP in the factory cars.
it'd probably cost you $5000 to implement now, if you have none of the MFI stuff, nor the cams.

there are probably faster, cheaper ways to get that 15HP, especially if you favor low-range torque.