What are the "Start & Acc" and "Pitch stab" circuit breakers for on the Piper Dakota?
It is for (two) accessories and the starter, they are on the same 15A circuit breaker. The page you want to look at in the POH is Section 7.17 (this is figure 7-11):



I know the image isn't all that clear, but the 15A breaker is on the right side of the alternator buss. It includes the cigar lighter, cabin light and starter solenoid.


  Why would the manufacturer combine the starter circuit breaker with cigarette lighter circuit breaker? If the cigarette lighter is not working in flight..is it really wise to mess with the starter circuit breaker?


I'm not sure why Piper put those two things on there, but they did. I don't see it as a problem though. If the cigar lighter isn't working that isn't a problem, you wouldn't mess with the breaker. If it is melting a hole in the dash then yes, you pop the breaker, hopefully you wouldn't need to use the starter in-flight. I would consider the need to pop that breaker (due to heating/smoke) an urgent situation (maybe not emergency, but I'd divert to the nearest airport). 

As for the "PITCH STAB", that is probably for an autopilot or altitude-hold system. The Dakota was available with a number of different autopilot options that operate separately from the electric trim system.