If you spend all of your $12,000 on a machine you don't need just because your worried about Uncle Sam getting his cut so the machine can sit around waiting to be used then you might as well set fire to 1/2 of your money. Uncle Sam, your county and your state will bend you over either way. Keep my $12k in the bank, sure I pay some to Uncle sam for income tax. I make less than $100k, have kids, house...deductions he won't get much. I buy a $12k machine, Uncle Sam gets his, my county/state dings me for a tax which they say is not a tax every year for the equipment I now own. With my $12k in the bank, Uncle Sam gets a nibble but my county/state don't get doodley.
If I had that $12k in the bank I could sit on it for a long, long time. I make money now, build things now, weld and fab things now with the tools I have. $12k in the bank while still being able to do my job and make money without a $700/month truck payment or a $200-300/month welder payment don't sound bad. If my machine lays down and I have $12k in the bank with more coming in then dropping $4k on a new welder or a good clean used welder would be easy. Uncle Sam is going to get his share regardless.
The guy you are talking about sounds like he was hard headed with a head full of jelly if he just didn't run down and rent a welder. Work on the broken one at night at the hotel while using the rental to keep that money rolling in. Scared into spending over $10,000 on a new machine that you really didn't need just because you saw another guys welder fail? I respect the heck out of you smooth but if I bought a new truck for every dodge, ford or chevy I saw on the hook I'd have the largest privately owned fleet of Dodge trucks in the world!!
Losing your spot? I live that everyday. Bid this job, price on that job and some you get, some you don't. Some cry cause your higher than the cheapo down the street who uses 1/2" square tube balusters -vs- 1/2" solid. Other contractors want you to rush right over and price out sevral railings then when you call them you can't get ahold of them and when you leave multiple messages they never call you back. I look at the huge global picture everyday and months in advance planning out what jobs are in the works, possible, money, bills and so on. I can "lose my spot" on any job on any given day regardless of what my machine does. Move on and find another one. Keep money in the bank so I can pay bills for a couple months at a time and I'm fine. Last year around January it rained like mad. Went out on the pipe job I was working and welder would not start. Guess the ol' gal got water logged from the down pours. Drove the 1.5 hours back to the house on my dime, loaded the ranger on the trailer and brought it back and started welding. Cussed a bit on the way but was nothing I could do, things happen. Lose my spot? Guess I'll go find another spot. This is why I would sit on that $12,000. You never know what is going to break or when and having cash on hand is better than having one extra of everything you own for the just in case moment and taxes.