I already own the Directors cut of the Witcher on Steam. What would be the advantages of repurchasing this on GOG?

None other than supporting the developers and getting a DRM free version

In 20 years time, when everybody has forgotten that such a service as Steam even existed, you will be able to play Witcher you bought on gog (assuming you have compatible hardware ;) ).

I have retail Witcher DVD, Impulse version, Steam versin and GoG verson (and I also pre-ordered W2) - seems I like to support CDPROJEKT :) And I don't even like RPGs that much :D

I bought my copy here primarily because I didn't have a copy and wanted it DRM free. Personally, I don't typically buy games here that I already own unless the other copy doesn't work properly with my computer.

If you want to support CDPR, you're probably better off buying TW2 anyways.

Personally, i did it because it is dirt cheap atm and it allows to play without something like steam running in the background. If you care about extra's, i believe the calendar extra is a gog-only one.

Um Steam won't be going anywhere unless the entire video game scene dies. Even if that happens I have full faith in Valve to take care of their customers since they are the best developer bar none.

What kind of extras do you get with the Steam version? The version here has quite a lot, including the soundtrack, music inspired by the game, maps, manual, game guide, a calendar, and more. I have heard that these are also higher-quality files than can be found elsewhere (for example, if you already have these things from Steam, the ones on GOG are higher-quality files).

Also, as others have said, GOG's version is DRM-free, very cheap, and will support the developers pretty much directly.

The main reason is for future compatibility...I don't know why nobody seems to get or value this. Buying here means the game will work on any OS indefinitely. Besides that you get a few extras other versions don't have, GOG support, and no DRM.

The PDF extras (guide, manual, maps, etc) are of higher quality than the steam versions, plus you get the artbook (also very high quality).

Well, I don't think you get as many goodies with the Steam version as you do with the GoG version. I could be wrong, but I don't think the Steam version includes the artbook.

But mostly, I bought it just to support CDProjekt. I bought the game when it first came out and loved it. Then I bought The Enhanced Edition, even though you could get all the enhancements for free if you have the original. Now I also have the GoG version, which I'm playing through again to refresh my memory before TW2. I've NEVER bought a game three times like this before.

Wow, finally beat The Witcher. There have been a few times I tried to play this and attempt to get through the semi-boring starter areas with no luck. This time I stayed dedicated and discovered an amazing game. Wonderful characters, plot, and gameplay.

Through I already own the CD and Steam versions, I wanted to support CD Projekt and thus bought it on GOG just now :) I'm enjoying the included soundtrack and art book, so they're nice bonuses.

I thought both Bioware and Blizzard are developers and not publishers. Also publisher is not same as developer :D

Steam version doesn't have the art book, short story or calendar. Plus other extras are better quality, Mainly the guide and manual are formatted for easier viewing. I haven't personally compared the other extras. Plus its only $5, its a soda and bag of chips out of a vending machine, give some support to the publisher if you like the game.

Personally I just never buy on Steam (well, bought TF2 once but it was my first and last), because that's supporting DRMs.
The 2 advantages I see from repurchasing on GOG are:
- get a DRM-free version, with perhaps more bonus contents (as per the others - I don't really care about bonus contents myself unless those are gameplay contents such as mods and such)
- support the good guys: the developers and someone who sells the game DRM-free
So, on a personal level I agree that this doesn't really bring a lot of advantages... I just bought it from GOG, but I didn't have a previous copy.