Hi, I'm new on here so here's a quick brain dump of my opinions on the subject - all open to debate, I hasten to add.
I agree with most of the points above, but R-M your Ferret argument doesn't stack up - you have to be a Lt with 5 years seniority to join DIS, so they are all grown-ups anyway. They then have difficulty completing all the background NGT basics like H&S, substance abuse, equal opps etc simply because they don't have drill nights. The alternative is to waste a weekend's ORT to fit in the NGT. Furthermore, the years of experience in the Branch isn't being passed on to the juniority because they don't have a forum to meet them regularly.
As far as the units go, they provide an essential RN footprint in non-naval areas (i.e. anywhere that isn't Pompey, Guzz or Rosyth) and the weekly gatherings provide an opportunity to foster teamwork and the Naval ethos in general. I agree that there isn't much specialisation training that can be achieved on a drill night, but for basic training, NGT and developing a sense of simply being the RNR, I believe that they are essential. There's also something of a paradox in that the New Entries and Junior Officers, who do gain useful knowledge and experience from drill nights, need the experienced people around to learn from.
I wholeheartedly agree that youcan get a lot more useful training covered in one weekend than six drill nights, but that's not the only thing we need to measure here. Don't underestimate the intangibles.
To sum up, there are good arguments for both weekends & drill nights. Perhaps we should be looking to shift the emphasis, rather than choose one at the expense of the other.