i think everyone can make use of a good drill... i am just an amateur mechanic as well as a very DIY-minded homeowner and like a few other folks above discuss, i've found that a good place to start out is a well-built, corded, 1/2" unit. you also might just want to spring for a hammer drill right out of the gate... that was one thing i kind of wished i had thought about more because now i have two drills; one hammer drill, one not-a-hammer drill. on the other hand, it's nice to have some variability in power and most hammer drills tend to be beastly.
the primary job for a drill in a garage setting (i've found) is probably drilling out broken studs/bolts and running screw extractors. so i think you are really going to want the power that the 1/2" corded units are going to give you when you are taking on steel, etc. i can't think of anything else you'd really use a drill for when working on a motor vehicle unless you are one of those people that likes to use a power driver on like EVERY fastener (edit: no offense intended just a difference in style). then, i guess go ahead and grab your box of hex bits and turn away. me, i prefer to use hand tools as much as i can and only bring out the "heavy equipment" if it's beyond my physical capabilities.
though, again, this is not how i earn my living. but you sound like a hobby guy, too. imho you can break a lot of stuff and round off a lot of fasteners with a power driver; if you're learning as you go, you get more of a feel and you can _develop_ that kind of feel for what you're working on with hand tools.
so i'd say hold off on buying the drill until you find yourself in the middle of a project where you need it. spend the money on some more sockets or a new ratchet instead

unless you are totally loaded up with hand tools, then, yeah, a power drill should probably be the first power tool in your arsenal.