I think that if you are constantly striving to do a better job, the job can't get boring. The challenge is to be more precise, to know more about the total operation with each flight.
In terms of destinations, for me at least, I am constantly going to new places. On this trip that I'm on alone, I either haven't been to some of the cities in years, or I have only been there once, and not layed over in some of them. Places like NAN, SYD, SFS,KUL, PEN, heading to SZX this afternoon now. The flying is challenging and the layoves spectacular. Just waking up now at the Shangri-la resort here in Penang. Look out my window across the Bay of Bengal, right on the beach, warm tropical ocean water, watched the sunset from a bar on the beach last night. Really amazing.
Let's not forget SFS, with non-precision approaches surrounded by mountains...Now, head to SZX, get to operate in the metric environment for altitudes, windspeeds, etc. Always interesting. Plus, I have a student on this trip.
I couldn't imagine this getting boring to me. Perhaps if I was flying the same domestic route where it got so I knew all the frequencies, etc., that would be a potential, but I think it is your attitude that shapes it mostly.