Missing hard drive is a non-issue... you can boot Knoppix or another live distro from a USB key -- it even gives you an option to create a persistent home directory on the USB stick. Probably better on battery life than having a hard drive, too. Otherwise, a new hard drive will probably run < $50. Heck, if it takes SATA drives, you could do a solid-state drive for about $60.
A quick look shows replacement Lenovo laptop CPU fans running $35 - $50; if you're handy with a screwdriver, I'm sure there are simple instructions to be found for replacing it.
Seems worth it, as long as everything else works -- laptops can be repaired reasonably cheaply if you're handy, but obviously the more parts you need to replace, the higher the cost -- at some point the ROI is too low to bother for a 6-year-old laptop.