This is what I think, and how I would go about it in deciding what is worth owning on Blu-Ray.
Movies I think should be owned on Blu-Ray and NOT just DVD, IF you got the DVD first before there was Blu-Ray of it. Also If you are getting it on any format for the first time.
Terminator 2: Judgment Day
Terminator Salvation
Gone With The Wind (Scarlett edition)
The Bridge On the River Kwai (combo one)
The Departed
Hard Target(when there is a Blu-Ray release)
Broken Arrow
Face/Off
Heat
Minority Report
Die Hard With A Vengeance
Miami Vice
The Untouchables
All 22 James Bond movies
Batman Begins
The Dark Knight
2001: A Space Odyssey
Leon: The Professional
Big Trouble In Little China
Bad Boys II(when there is a Blu-Ray release)
The Fall
Planet Earth
Life
Human Planet
Snow White And The Seven Dwarf
Fantasia
Dumbo
Cinderella(when there is a Blu-Ray release)
Peter Pan(when there is a Blu-Ray release)
Lady And The Tramp(when there is a Blu-Ray release)
The Little Mermaid(when there is a Blu-Ray release)
Beauty And The Beast
Aladdin(when there is a Blu-Ray release)
The Lion King
Fantasia 2000
Finding Nemo(when there is a Blu-Ray release)
Who Framed Roger Rabbit(when there is a Blu-Ray release)
X-Men First Class
X-Men Origins: Wolverine
Despicable Me
Rango
Wallace & Gromit: The Complete Collection
The Magnificent Seven
The A-Team (ONLY if you are getting the Target exclusive, which is a Blu-Ray DVD combo)
Cop Out
National Geographic: In the Womb (when there is a Blu-Ray release)
America's National Treasures
The Guns of Navarone
Collateral
Cowboy And Aliens
Kung Panda movies
These are the movies, I think one has to ask him or herself is Blu-Ray needed or DVD is just fine already upconverted(some will say yes and some no).
Gran Torino
First Blood
Rambo: First Blood Part II
Stealth
Dirty Harry
Raw Deal
Eraser
Casino
Donnie Brasco
Once Upon A Time In America
The American
Wall Street
Narc
Training Day
Dark Blue
We Own The Night
Street King
Pride And Glory
Brooklyn's Finest
Bruce Almighty
Fair Game (2010)
Spy Game
The Peacemaker
Celine Dion: A New Day... Live in Las Vegas
Andrea Bocelli: Under the Desert Sky
The Blind Side
Outbreak
Cirque du Soleil Flow - A Tribute To The Artists Of 'O'
Oceans Eleven (original and remake)
Oceans Thirteen
Bounty Hunter
Die Hard
Die Hard2: Die Harder
Live Free Die Hard
Batman
Batman Return
Batman Forever
The Social Network
Bad Boys
Town
Vivere: Andrea Bocelli Live In Tuscany
Celine: Through the Eyes of the World
Keeping The Faith
From Paris With Love
The Bodyguard
True Grit (John Wayne one)
Rio Bravo
Road Warrior
Backdraft
Unknown
Final Fantasy VII: Advent Children
Cirque du Soleil: The Mystery of Mystere
The Good Thief
Lucky You
Rocky
Legion
Blade Runner
Star Trek movies
Days Of Thunder
21
Yonkers Joe
Island
The Fifth Element
Paul Blart: Mall Cop
Serenity
Salt
Universal Soldiers
Layer Cake
Powder Blue
Contact
Dune
The Matrix
Back To The Future movies
Cirque du Soleil: Journey of Man
Viva Las Vegas
Jail House Rock
Scarface
Super 8
Thor
No need for Blu-Ray AT ALL, DVD upconverted is good enough already(everyone would agree).
Shaft
Shaft(Samuel L. Jackson one)
King's Ransom
Even Almighty
8 Miles
Zoolander
Menace II Society
American Gangster
Juice
Dragonball Evolution
Street Fighter: The Legend of Chun-Li
Power Ranger Movie
Righteous Kill
Dreamgirls
Soldier
Semi-Pro
xXx: State Of The Union
Little Nicky
Universal Soldiers: The Return
Universal Soldier: Regeneration
Universal Soldier: A New Dimension
Harlem Nights
Vampire in Brooklyn
A Rage in Harlem
Timecop 2: The Berlin Decision
Bloodsport
Death Warrant
Takers
Big Daddy
Ultraviolet
I Know What You Did Last Summer
Scary Movie
The Happening
Queen of the Damned
Get Rich or Die Tryin'
New Jack City
Proof of Life
Mad Money
The Golden Child
Bruno
Napoleon Dynamite
Donnie Darko
Obssed
Waist Deep
Red Planet
Get Carter(remake)
88 Minutes
Bridesmaids
Assassination Games
Abduction