That depends on whether:
1) the patch is high-quality and works for most users
2) the rightsholders permit to do so.

Old games need unofficial patches that you have to look for. You'll just have to live with it. There are very few exceptions to that, like Thief 1/2 and System Shock 2, which use the fan-made NewDark engine that greatly improves performance on newer systems, and GOG and (if I'm not mistaken) Steam versions have them by default.

Check the stickied threads in the respective game forums.

There is a reason GOG can't officially provide fan-made patches. Getting them here might be a legal nightmare in the first place, and even if GOG manages to do so, they'd have to provide support for them, which would be a whole new can of worms. They are "fan" patches for a reason; stuff that players, usually without access to the game's source code, hacked together in their spare time.

That aside, I'd disagree that they are "are very needed in 2017". A lot of us came here to play good old games just like they were in the good old days. With all the pixelated graphics, 4:3 screen ratio, beepy sounds and terrible controls. If I want new games, I buy new games, but with old games all I want from it is to run properly under DOSBox with a normal speed and I'm happy as a clam.

Thing is they were not pixaleted at release date. You had monitor with 1024 not full hd and 4:3 ratio. I think many old games still look nice BUT would be great if they can adapt to hardware.

No one was angry at HoMM3 HD for being remake, only for not having addons. So many ppl enjoy OpenTTD or CorsixTH etc etc simply because they are old games but adjusted to new hardware.

Dunno if having link to unnoficial patch in Galaxy would make any law issues

They were, it was just not as noticable on the dotted display of old CRT monitors. OpenTTD is very much different from the original Transport Tycoon. Not only is it an entirely separate engine, it also has some features that the original lacked.

Yes, they were. With CRTs it didn't stand out quite as much, but it was still readily apparent. I remember going from 320x200 to 640x480 or even the gobsmacking 800x600 and what a huge difference that made in clarity alone. The change in resolution is the only thing that made games look less "pixelated."

Sure but thats the point i made. Hardware changed. You had 1024 on 15-17" probably (suually 15") now standard is 24"-27" so it cant be compared in visual comfort. Old game displayed on 10" tablet is still looking good when on 27" is crappy ;]