Replay value?

I finished Batman: Arkham Asylum last week.  Rather I finished the Normal Story mode.  But the game is not complete without getting the Platinum trophy, which requires replaying the game on Hard, plus earning medals in the challenge rooms.  Half of the challenge rooms are pure brawler the other half are stalking rooms.  I love the stalking aspect of the game, but the brawling....meh.  Plus there are Riddler Challenges yet to complete.  The Riddler Challenges are probably one of the coolest parts to the game because you can get so much backstory on Batman and the various enemies he has faced over the years.  The problem I'm facing right now is I have completed 238 out of 240 Riddler challenges.  The last two I need to complete are elusive.  You need to destroy 20 chattering teeth in the different zones of Arkham to complete the Riddler challenges.  In one section I have 19 of 20 and in another I have 17 of 20.  I have slummed through the incomplete sections twice and can't seem to find the last 4 chattering teeth.  Ugh. So for the sake of "replay" value I find myself hunting for trophies in sections of the game that I have completed, basically wondering the halls of Arkham, now empty, and find it boring.

I'm not sure that I want to replay the game on Hard and I can honestly say that the challenge rooms aren't my cup of tea (except for the stalker rooms--that was the best part of the actual game).  I may go back to Batman at some point in the future.  But I still need to actually finish Star Wars Force Unleased, something I'm not sure I really want to go back to.  Sam beat the stinking game in one day.  This is the second time that he has finished the game.  I have yet to beat it.  I have been playing it on Normal.  I think he has been playing on Easy.  Curse my need to collect trophies.  I find myself going back to Batman because it is fun, even though it is challenging.  Force Unleashed is not fun and annoying.  If there was a way to set the game on auto pilot simply to be able to see the story unfold I would put the game in and play through for sure.  I suppose there are other games that I could go back and re-play or finish.  All for the sake of trophies....so do they add replay value or just a big headache?

I'm not sure.  Maybe both depending on the game.