A wise man doesn't need a full toolbox.
"I'm just not sure we're using the best (ie. widest) range of tools."
Of course not. Think about it this way ... How many people have the know-how and all the tools necessary to repair all the little things that go wrong around the house? How many people have the tools and know-how to build any new tool that they need? How many of us are tool & die makers and/or blacksmiths?
Plumbers, electricians, carpenters, roofers, and HVAC folks all have their own problems, and the tools to resolve them. I'm sure you can hang a bookshelf ... but can you build a shed, and install a generator and transfer switch according to your local building code? Would you attempt it? If you did, would it pass inspection? Would your insurance still be valid? (I have, because our horses are on well water so we need power 24/7 ... it's not all that difficult, if you talk to experts first.)
Do you want your next-door neighbor's kid, who completely restored a 1959 VW Bug, working on your brand new 7-series BMW? Come to think of it, do you want the kid who recently passed (with honors!) the BMW technical school working on your '09 Learjet 60 XR?
Why should computers be any different?
I'm NOT saying that people shouldn't have a wide variety of tools available to them (I'm an old UN*X hacker, the more uni-tasking bits of code you give me, the better I like it ...).
What I am saying is trying to specialize in all of it is a fool's errand. Computers are the most complex bits of kit that good ol' HomoSap has ever invented. There is NO WAY to understand computing in it's entirety. Rather, you're better off picking a couple of Swiss Army Knives that'll get the job done with a minimum of hassle.
C is, to the best of my knowledge, the best all-round tool in the programmers toolbox. Don't get me wrong, C is not the best tool for every programming job. But it'll work in a pinch in every scenario I have ever seen, under any OS, and on any hardware. I can't say that about any other computer language.
Should a programmer have many tricks up their sleeve? Of course. Should they know when one of their other languages is a better solution than C? Of course. Should they continue to learn new languages indefinitely? No. Not in my opinion. At some point you'll hit the point of diminishing returns ... which by definition is negative-flow.
Taking it back to automotive analogies (not perfect, I know), a friend of mine is the best wrench I've ever known. I've known him since we were about 12 years old. He was my mechanic when I owned an OMC dealership in the Port of Redwood City. He has taken it upon himself to collect as many tools as possible "just in case". Large tools, small tools, machine tools, hand tools, electric tools, pneumatic tools, hydraulic tools, diagnostic tools ... Name it, he's got it. He can work on wood, glass, metal, fiberglass, plastic, the land ... He has rebuilt railway cars, boats large (200ft+) and small, cars, motorbikes and trucks (large and small). He has restored houses (mine) and added onto them (again, mine), and ripped up and replanted a pest ravaged vineyard (again, mine ... our first batch of wine from that is aging (finally!)). If man has built it, he can probably fix it.
Unfortunately, his tool collection is now so large that he needs four 40 foot shipping containers to house the bits that need to stay out of the weather; the weather-proof bits would make a largish equipment rental yard jealous (I know, his collection is behind one of my barns ... It took seventeen trips with a heavy equipment flatbed to get the weather-proof bits here). Keeping it cataloged and in good repair is a full time occupation. I only had him work on my house to keep him out of the poor-house ... He's got so much kit that without my ranch for storage, and to keep him busy, he'd spend so much time taking care of his collection and paying for its storage that he'd go broke. I'm trying to convince him to sell it on ebay ... He must have close to 10 million dollars worth of stuff that is mostly unused ...
On the other hand, I have a basic set of Craftsman tools (probably $4000 to replace), some basic woodworking, electrical and plumbing tools, three welders, two compressors (one portable, one in the tractor shed) and their attendant tools, large, medium and small tractors (with just over a dozen total attachments), a riding lawn mower, three chainsaws, a couple weedeaters and a water truck ... and I manage to properly maintain a largish horse ranch without going to a rental yard more than a couple times per year.
Sometime less is more ... The trick is to pick which less to learn in it's entirety.
Or as Granpa used to put it "A wise man doesn't need a full toolbox" ...