Extra Pieces of loot is not going to help 25 mans become on equal standing with 10 mans in popularity or desire to raid, and you know why not ?
Because the same stuff drops in the same instance in 10 mans. The majority of people will take the route of least resistance.
Why should someone join a 25 man raid, when they can get the exact same loot in a 10 man guild and probably get it quicker due to less people rolling on on items, or above them in what ever priority system is employed by the guild ?
There is only one real solution to the situation besides changing format to a 15 man size. That is go back to the WOTLK style of set ups.
No its not ideal due to many guilds feeling like they are forced to go to 25 man for better gear but it worked, there was a good amount of both 10 and 25 man guilds.