I disagree with Anne, 25 man raids do not need to embrace what is unique between the raids: the only thing that is different is the ratio of the roles, the quantity of loot, and the amount of people involved.
In fact, the biggest perk I see of being in a 25 man is that you can gear up faster, you can get legendaries faster, and if you have an off night, someone else is able to make up the difference.
In my 10 mans, if I'm not firing on all 10 cylinders, then a boss might not die. When I was in 25 mans, as long as I was in the top 10, no one said anything to me, even though it was obvious when I wasnt really concentrating.

The reasons I dont do 25 mans anymore is the people issue. Getting 28 people (subs), all with geared offspecs, most with alts that perform different rolls than their mains, all with personalities that jive together.... its a monumental task. In fact, the reason I left my last guild, which was a 25 man guild, was because there were 5 people that insisted on acting like asses, talking about stuff that made me feel uncomfortable, and when it was brought up with officers, I was told to relax.

I cant suggest any one thing that might fix it, but I think 25's already get everything extra that they should: its the community, or the lack thereof that is making 25s die and 10s flourish.