Buying tools is a love/hate thing for me. I like having tools, but REALLY have trouble spending money on tools. For years I've had a policy that if I have to borrow a tool from a co-worker more than three times, it's time to buy that tool. Lately, I've reached the point where needing a tool only one time often justifies buying it. I've learned that if I need it once, I'll probably need it again in the future. So I buy it, as long as the price doesn't involve more than three digits.
My customers are in a different situation. I'm not sure what I'd do if I was working on only my own equipment. I've seen farmers who have tool supplies on par with any professional mechanic, and I've seen farmers who's entire tool inventory was composed of three hammers and a Crescent wrench. I suppose it comes down to whether or not you enjoy working on things. If you get satisfaction out of maintaining and repairing things, then you'll enjoy owning tools, especially specialty tools. But if you begrudge any time spent with a wrench in your hand, you'll resent any tool beyond what's necessary to do an oil change in a tractor.
This whole debate about buying tools was renewed in my mind when I recently moved to a different shop building at the dealership. The move unearthed a lot of tools I forgot I had. Do I regret spending money on tools I used only once or twice before I forgot I owned them? A little. But it's better to have a tool and rarely use it than to need a tool and not have it.