Diagnostics uber alles is as silly as the opposite. Throwing parts at a problem is very often a viable solution - if the part is old, the replacement cheap, easy to replace yourself, and a possible solution. A shop can't really do it - but for a DIYer it's often the way to go, especially if the part costs $5 or $10 or $25, etc. and you plan to keep the car for a while. Do it for a few years, at a cost of no more than a few hundred dollars, and you will have a very strong reliable car. It's the pure extremes that get silly - diagnostics all the time, or throwing parts all the time. There is nothing worse than paying a shop for inconclusive diagnostics and then throwing parts at the problem, which happens more often than you think - as evidenced by threads on this forum. This would be different if diagnostics were an exact science but it isn't - far from it.