Primary symptom would be a loss of power, if the valve is really tight, it will only idle or turn up to a few thousand rpm then either die outright or chug along. It's primarily the EXHAUST valves that are going to get to tight, they run much hotter than the intake valves. With the valve not being able to fully 'seat/seal' exhaust remains inside the combustion chamber greatly diluting the incoming fresh air/fuel mixture, thus reducing horse power. More tight, more reduction of power, mpg suffers as well. Think of it like slowly being choked to death... Based on MY experience with small engines/motorcycle engines a burned valve or serious damage to the head/valve is unlikely. The motor simply slowly looses power over time until it has lost virtually all it's power if the valve gets tight enough, adjust back to specs and your 'good to go'.
MULTI cylinder engines are more problematic than a single piston setup. Like a V6 or V8 with ONE tight valve, you may not sense the loss of power in time to stop engine damage, because the other cylinders provide 'enough' power to keep going. Thus you drive on and ruin/burn the one bad valve. Motorcycle engines (two to four cylinder) are small enough you DO sense the power loss early on and get it fixed before damage occurs.
Slightly tight valves or valves adjusted to the 'tight' side of the specs make MORE horse power than loose valves. Thats one reason you sometimes hear a guy say, "Man it was running great, never better, just before it blew up." The valves may have gone from 'tight and right' to 'to tight and bad'! Or the piston crankshaft clearance was nice and 'loose', like just before it let it go!