I admit that, having an affinity for startups, rather than more traditional small businesses, I have a greater affinity for risk. Ironically, perhaps, I'm usually the voice of risk-aversion with respect to IT infrastucture, so I don't believe it affects my overall understanding.
I recently pointed out to an interviewer who was trying to convince me that it was worth spending half a megabuck on a petabyte from Netapp because it was "business critical" instead of 1/10th that amount for DIY, that, just like the DIY solution, Netapp does not indemnify the business against loss. One isn't buying insurance, only a bunch of technology.
Sure, "works the first time" is worth something. Is it worth the cost of a whole, complete, extra server on a order of qty 6? If the infant-mortality rate on servers is anywhere approaching 1-in-6 and they're being shipped somewhere that the replacement time and/or cost would be prohibitive, I'd still probably rather just order 7 servers instead.
That's my main problem with paying a vendor for "reliability": it's a very fuzzy, hand-wavy assurance. Paying for reliability with more hardware has data and statistics behind it, which is an engineering solution.
I agree with your cautions around supermicro resale but the warranty support and build diligence are absolutely necessary for a small business. Having a good business relationship with a trusted provider of hardware that always performs the first time is priceless.