It might be worth it to rebuild if you are a collector of old receivers, speakers and such. I myself have several old Sansui, Marantz, and Pioneer receivers that I like to swap in and out of my basement vintage system, along with various old speakers such as Pioneer, Dahlquist, EPI, University, Yamaha, Wharfedale, Infinity, Bose, etc. It's fun to listen to different setups while I work on my latest project - and all of the above have been (or will be) projects at one time or another. The most I paid for any of them was $50 (plus whatever it took to fix them up).
I don't fool myself that I will be able to reap huge profits by selling them, though. I always feel a little guilty selling any of them, actually - it's like selling my kids.