You're probably right, but I just don't have time to do anything more when I'm running lots, i.e 4/5 times week in build up to FLM
I followed the runners world marathon training plan from mag OBSESSIVELEY! Worked for me first time round, but think I'll be slightly less obsessive this time! E.g if it said weekly total 32miles, and I'd only done say 28 - I thought that was DISASTROUS, and even though I stuck to MOST of it religously, I was extremely wound up that I'd probably fail because I'd cut the very occasional session a tiny bit short!
That said,I think the VERY long runs are critical, and I did 2x20, 1x 22, along with 2 18s which was more than reccommended, but would again be nervous of doing much less as it worked and got me round reasonably comfortably.(ie didn't collapse over line, and actually enjoyed the last mile!!!!) Huge sacrifices re family for quite alot of Sundays!!
The other thing I'd reccomend is to do a couple more half maras - say Autumn and Spring; can be v motivatin especially if your time improves. Also a couple of the big spriong halves have RW pacers so you can practice "hanging on in there!" Was complete beginner myself pre FLM, with just one half under my belt, so go for it!!