Deciding on Matt or Karl's advice

I think alot of runners get to a point where simply finishing a race is just not enough for them anymore. Maybe they've been at this for a few months or maybe even (like in my case) years, but one day it just hits you. Gee it would be nice not to be last all the time! Personally I would rather spend 6 hours out on the trails than 8 during a 50 km. So, how does one get faster at running long distance? Run more? Run less but with more focused intensity? Both? Running legend Karl Meltzer has said in a few different interviews that he would recommend just running more, for long periods of time. Matt Fitzgerald seems to advocate a minimalist-with high intensity-approach. Is there a middle of the road?
In search for that happy medium I've been researching triathlon training plans with a focus on the run portion. No, I don't actually plan to run a full Ironman, but the high intensity approach seems to work for those who are biking 100+ kms then jumping off to run a full marathon, so would this approach work for 50 km trail running? I like the idea of all the cross training (biking and swimming) that would be built right into these plans, I think it would help reduce injury and keep the mind fresh over the long haul. Currently I just try and carve out a few hours each week to get some random strength training in and a scheduled 45 minute spin class every Monday. Oh the decisions!
I have to say, it's not like I'm looking for a shortcut to my training. Currently I'm training, either running or cross training for a total of 9 hours each week (give or take an hour or so). The triathlon plans I've looked at (the minimalist ones anyhow) have their athletes training for about 10 hours a week, so there's not much difference, only I'd be spending more time in the pool or on the bike when currently I'd be running.
I think my endurance is also something to consider, I know I can spend a day (8 hours) outside running-not at top speed mind you-but running/walking nonetheless. If I couldn't do that then I would stick with my ultra runner plan.
So I guess it comes down to my fear of missing some crucial training element by switching to a tri plan rather than sticking with my ultra runner plan. Can I get faster by running more focused, high intensity runs? Can I get myself to the middle of the pack instead of the rear in these trail races? I'll let you know :-)