Hi Roamer, dont bother with the head, its fine, and NEVER have one polished.. (thats just for show and no go - Sorry Fred lol!)
this is enforced by the FACT that the restriction on the 172 IS THE INLET MANIFOLD and SYSTEM design as a whole.
Yes, tbs are the way to go, you should get a good 215-225 setup correctly.
you will need an aftermarket ecu though which adds to the cost.
Most people chose choke sizes that are FAR too large, select the size correctly and you will have a superb, tractable unit. (It will be as good, or indeed better around town than it is now m8!)
Dont change the cams, not worth it...
Joe.