I've found that owning and using a Mac, even 'old' ones, can be of great help in solving customers' problems with theirs.
I'm using a PowerMac G4 MDD at my main desk at work, attached to a Cinema Display of the same approximate vintage. I know it might sound crazy, but other than its slow video performance, it has been fun and reliable. You learn the little stuff that makes it unique, like their open firmware/EFI, and ways of solving all sorts of 'weird' problems, e.g. clearing NVRAM/PRAM by holding P-R-Command-Ctrl keys at startup (the keys are different on some Macs, IIRC). I should disclose that before this machine, I received an iBook G4 as a gift, back in ~2005-ish. That machine, which I still use, is my first Mac.
IMHO, the greatest thing is that ALL of the documentation for virtually any Mac that comes in the door is all available, usually through Apple, or at least from sites which specialize in Apple repairs.
I've had very, very few customers ask whether I repaired Macs. The only Apple products which have come in the door have been half-demolished iPods and iPhones, their owners wondering whether I could fix them.
"Errrr....no, sorry. See that bit hanging out the side? That WAS its circuit board."
If any Macs do need repair, I'm no longer apprehensive at all about servicing them. But I don't even attempt the stuff I'd classify as 'consumer electronics' instead of 'computers and CIT-related' anymore, such as the aforementioned iPods and iPhones. I've found them to be too time-consuming for my current operation, and thus the labor cost too high to justify repairs in most cases. Same for the replacement parts; sometimes they're more than half the cost of a whole new product.
EDIT: Forgot to mention, I've also 'revived' two Xserve servers, one PPC G5 and one Intel w/ Xeons, plus their accompanying Xserve RAID boxes. These guys were a HELLUVA lot different than any Mac I'd ever serviced before! A very cool, if not trying-at-times, learning experience.
FWIW, I'd highly recommend using Apple hardware when connecting to a Mac, e.g. use an Apple keyboard, mouse, and display if possible. Your best bet for solving most problems is to simply sit down and RTFM. Apple has done an excellent job of documenting their devices' installations, services, and repairs.