I don't think so. As with any drug abuse, your body develops a tolerance to caffeine. Over time, you develop a drug dependance on caffeine; you require more caffeine to feel as awake as you did before your drug dependance developed. Thus, there is no net beneficial effect.

The pleasure experienced while consuming products that happen to contain caffeine is a beneficial effect, no matter what the study says.

It certainly is. However, don't discount the corresponding hangover period.

Since there is no time-averaged gain in pleasure, presumably the benefit lies in being able to time the pleasure, say to compensate for mood changes due to other factors.

Net zero? No. This proof you have constructed is ridiculous.

Steroids are the same in these regards. Your body builds up a tolerance. When you let your blood levels of the drug drop, your testosterone production is lower than pre-drug.

So these must cancel out right? Heavy steroid users must be the same size as weight lifters who worked as hard without the drugs?

Yeah. Caffeine wakes you up when you start taking it, allows you to function during the period when you're taking it regularly, and makes you drowsy when you withdraw from it.