i believe you asked for our thoughts on this... so here goes as little as it's worth these are my thoughts....
Secluded valley right now is pretty easy.... but it is the first ascended dungeon so i would keep it easier than the others as an introduction to the ascended modes.. that said i would add some more difficulty to it with mechanic changes not really more hp/harder hitting mobs... so keep everything the same except.....
Boss 1 (the snake) give ability to respawn add's
Boss 2 (the dog) give an agro reset mechanic
Boss 3 (the gaurdian) give his add's invulnerability untill the gaurdian is dead or at X% hp
Boss 4 (the ghoul guy) Change his sleep to a "take control of" ability for say? 20-30 seconds?
right now you take out the add's then tank and spank the snake (lol.......) no difficulty or tactics there but if the add's respawned then would add a bit of difficulty killing the boss before he enraged.
The dog is and has always been tank and spank he can kinda hit hard to non tank party members so if added agro reset then would make it just a little harder but not too hard
The gaurdian again same as snake kill adds then tank and spank the boss..... make add's invulnerable untill boss was dead or at certain Health also make them heal the boss but able to be silenced/stunned/rooted (and can kite boss out of range of their heals) add for some tactics in game play.
The ghoul kinda have to watch out for the cannon drops but not tooo much... now if the sleep was changed to take control of target (make it be AI controled and an enemy for X seconds) then would be a lot more fun... and interesting he might grab the tank so otehrs would agro or he might grab the healer so ppl have to go without heals for 20-30 seconds or might grab dps making us take too long to kill and enrage or what ever... would be fun.
the other ascended dungeons though should be even harder... both in dmg dealt and mechanics they used.... infact i would love to see ALL 3 bosses at the same time for the TR ascended