When we had the valve replaced on our '66 Newport (back when Chrysler still built the parts to do that), when reassembled, the supplied bronze bushings for the exhaust manifold were "tight" and didn't allow the shaft to move fully with just thermostatic spring tension. So, the shaft was removed and the bushings reamed so the valve moved freely and easily.
Typically, the valve will remain mostly closed during normal operation. The spring will keep it that way, until exhaust flow opens it. The valve plate is slightly off-set to help move the counterweight to open the valve. The earlier ones had such a counterweighted system, but later ones just had the spring with a round "weight".
So most valves will stick in the 1/3 open position, from my experience. It sends exhaust heat up through the intake manifold's "heat riser passage", which is ALSO where the carb's automatic choke thermostat is located! If no heat goes up there, then the automatic choke won't come-off as soon as it should, which can cause poor performance and fouled spark plugs. 318s that only see town miles will eventually coke-up the passage, which will require the manifold to be removed and the accumulation chiseled out (which many '66 Belvederes the local dealer sold to older ladies needed after a few years of operation, just to get the automatic choke to work.
So, get things free'd-up to get the shaft out of the manifold. Ream out the bronze bushings (which should be the friction interface between the cast iron manifold and the steel shaft) so that the cleaned-up shaft will move freely in the bushings. This is important! Then reinstall everything with some high-heat lube. THEN, every oil change or so, make sure the valve is working freely.
IF you have a carb with a full electric automatic choke, then no exhaust heat to the intake manifold passage is not a big deal.
The OTHER function of keeping that passage working is for fuel atomization in the manifold plenum, during warm-up. Until the engine block's heat convects into the manifold itself. An aluminum manifold tends to quicken this, though.
In our moderate N TX climate, I never could tell one way or the other if hot restart performance was really affected. Of if normal drivability was really impacted with the valve being just less than 1/2 way open/closed. Never did need to get much past 1/2 throttle anyway.
Consider the heat riser valve to be a part of the supporting cast of characters for efficient engine fuel system performance. Take ONE part out and it can mean the rest will have to be re-tuned a bit to compensate.
By observation, Chevy engines also have had heat riser valves, too. Even the 6 cyl engines. Most stuck about 1/2 open/closed, too. No starting issues that I have known off. Generally didn't get fixed, either.
My '77 Camaro had a heat riser valve that was vacuum operated, which I thought was a plus. Keep it working. Until the linkage fell off after several 100K segments. Ball stud wasn't round any more. That valve made a big clanging noise, due to exhaust flow pulses in the manifold. Certainly NOT a smooth flow! Which is probably why Chrysler used that "couinterweight" to dampen the valve's rotation against a spring.
Just some thoughts,
CBODY67