Wejo,
I had a stretch from 2004-6 in which I ran 6 marathons a year, and that was a bit much, but I've been doing 2 or 3 year since then and find it very enjoyable.
Having an event - and a trip - on the horizon provides motivation and a schedule that might otherwise stagnate. Marathons are a great reason/excuse to rally a group and get to an interesting destination.
I'm not especially quick with a best of 2:42, nor am I into high mileage with a usual schedule in the 50's per week. So that doesn't necessarily tie in with "more is better" in the short term. However, I believe in another sense that more events and destinations are indeed healthy since they can lead to sustained participation. I also think the relatively light schedule (at least relative to many letsrun posters) has prevented burn out, and made continuity much easier since at ~1 hour per day on average I'm not really giving up much with work, socially, or other hobbies to train. As nice as a 2:3x would be, I'm just not going to sink the miles and time into chasing what I believe would be at most 10 minutes faster. Nothing against people who are pursuing their absolute best, but I personally see few of them who end up content with what they've done, and fewer still who stick with it.
I'm not on board with the 50 staters or the folks who lead pace groups every other week, and I'd be interested to hear what motivates them. Mixing and mingling is great, and I may not always be shooting for a best, but I'd rather pull my toenails out than run 2 minutes per mile slower. For me its a way to integrate exercise, travel, and challenging but reasonable goals to stay interested and enjoy it.
btw - I've done New York twice, including capping a 3 marathons in 4 weeks stretch a few years back with a hobbled 2:45 finish. That was too many. I took a good while before getting back into it, and it did frankly get me believing that the notion of only have so many hard marathons in your legs has some merit.