... The Friday Night Ride to the Coast deserves honourable mention, I think, as it does a particularly good job of it. I'm not sure whether that's because it appeals to us weirdos, or because riding at night is a good way to avoid traffic without being limited to closed roads and cycle paths, or because overnight rides make things like childcare a lot easier to organise. ...
Having said all that, the FNRttC doesn't get particularly high numbers of women, when I've looked at the numbers and made an estimate on a ride, it's always been around 10%.
The Lambeth Cyclists Architecture rides, which someone else mentioned, do seem to get more women than that, and I haven't been on one for ages, so this is all based on sketchy memory, but they're probably still predominantly men.
The only rides I've ever been on where women are present in anywhere near the numbers that men are, are ones with only a very few riders on, which just makes it a statistical anomaly. Even YACF rides of any significant numbers, whilst they probably have more women present than is common in other rider, still tend towards being predominantly male events.
Assuming that you see encouraging more women into cycling to be a good thing, I'd and say it is, then I'm not sure what's the best way to improve this. Cycling events as described in the OP would seem to be an approach, although clearly one that doesn't appeal to some on here (but as has been said, probably not the target audience), but it does worry me that this could possibly lead towards a more entrenched position on going on such rides.