If it is a great film first, one that warrants a second viewing at the theater, then it is certainly a worthwhile enhancement to the film for re-release.

But it can't be a cheap gimmick for a poor film, even if done on its first release (Clash of the Titans anyone?).

As a movie buff there are plenty of films I'd love to see in the theaters again, and WAY MORE that I'd like to see for the first time on the big screen.

One thing that is very cool about 3D conversion of older films is that it is a way for the studios to re-release older films that would normally never get another chance on the big screen.

Here's a quick list of movies off the top of my head that would be awesome for a 3D re-release...

ALIENS
SUPERMAN
ARMAGEDDON
STARSHIP TROOPERS
SCARFACE
A CLOCKWORK ORANGE (for all of Kubricks slow forward moving perspective shots)
2001: A Space Odyssey
BACK TO THE FUTURE
TERMINATOR 1 and 2
GRAND PRIX

Okay off the top of my head thats a start.

I can't help but think of the Orson Welles quote, “Keep Ted Turner and his d*mn Crayolas away from my movies.”

I think the same is true for 2D vs. 3D.

only in animated films or with heavy computer graphics use like 300, watchman or the matrix .....

No, the current 3D movies are still not of the best 3D quality at all. First try to improve the 3D quality of current movies and those who are in the making, before even attempting to convert old and surely the classic movies to 3D at all.

Anyway, at the moment I don't even like 3D movies. The current 3D movies have a few scenes which are excellent in 3D the rest is converted from 2D to 3D and look like cardboard figures and object in a shoebox you made in kinder garden.
Which are not worth looking at or even paying extra at the box office.

I would like to see The Lord of the Rings Trilogy and JJ Abrams' films Cloverfield and Star Trek only in IMAX 3D - assuming the conversion was exceptional.

This most recent incarnation of 3D leaves me cold. OK, Avatar was quite good in 3D, but everything else I have seen has been underwhelming. I'm not sure which movies were shot in 3D, versus those that were post-converted - and maybe that does make a difference - but I no longer bother to pay the theatrical 3D premium. Even though my current flat panel came with 3D capability, it has become an increasingly incidental feature (would I have to pay a premium for a TV without 3D? :)) - so I voted to leave older movies alone.

I think "Plan 9 From Outer Space" would be GREAT in 3D. For those drunken movie parties, anyway.

There's a lot of other things that went wrong other than some type of substitution pattern. -James Stuckey-Amor

I would like to see any 2D animated movie out there converted, but I know that probably that it's not a good idea for all of them. So I would go for the second option, I think 3D conversion is worthwhile for some movies, the more recent ones to be more exact.