Lars the Apple technician at BeachMac is terrific: honest, hard-working, and a professional. He called me the day after I dropped off my constantly-stalling laptop to give me a technical diagnosis, a cost estimate of various options, and his final recommendation (install a solid state drive and upgrade my operating system).
He explained that while my laptop could use more RAM and a new battery and he'd happily install both, neither are urgently needed. So I passed on both, and saved ~$300.
Most importantly, my laptop is running beautifully again.