There is certainly merit in this idea, especially if you follow the golden rule:
"If it isn't right, throw it in the bin"
But there are several reasons why it also falls apart as an argument. First and foremost amongst these I guess is that as you would expect the most satisfying cameo layouts tend to be those built by the most experienced modellers. You'll find a fair few listed in my links section. Undoubtedly the micro-layout is considered a legitimate branch of modelling. But you'll also find a big gulf between these models and the run of the mill micro-layout where all too often the format seems to be an excuse for unrealistic whimsy and poor workmanship. At this point I have to declare a certain affinity for whimsy of the Emett persuasion and a track record of poor workmanship. Do as I say, not as I do.
The truth is that the format means any layout will be subject to close up scrutiny, and the evidence of a lack of skills will be all too visible. Because the whole layout can be taken in in one view, and because for effect a diorama depends on all the elements working together and one element being sub standard will ruin the illusion. In contrast a larger layout gives you more room for the mistakes to get lost in the bigger picture.
The other issue I have is how many useful skills can you actually learn in building a very small layout? Undoubtedly you can try out a very limited range of scenic techniques, and some basic track laying and wiring but that's about it, and to be honest trying to learn those techniques in the small space of a micro layout probably isn't the best idea. Esoeciually when you take into account the time and cost involved....