I think you'd be surprised with how many would buy a copy and return to it even said return is fleeting for some, as nostalgia is a powerful thing. I run the Colonization and Master of Magic fan communities and they were ghost towns when the games weren't available anywhere (except on abandonware) but once they arrived on GoG and then more so on Steam (due to it's market dominance) it was just a game changer and it's guaranteed a steady flow of returning players coming to the groups to talk about the games and grab mods etc ever since. Recently EA released all the classic C&C and Red Alert games on steam and it was crazy as thousands of people bought copies and flooded the C&C communities posting about how happy they were to be playing the old games again, which of course attracted comments from the veterans/regulars saying "what is going on around here??.. EA released these games for free a decade ago and free legal copies of them are on all the fan sites??".. and the answer is Steam aint just a site that sells games, it's also a massive marketing platform that reaches so many people, and so when a big publisher releases a bunch of old games (you'd think everyone would already have or has forgotten about) it usually makes mainstream gaming news and brings in all those casual gamers out there who don't know the things the hardcore fans do and can't resist buying that game they loved so much when they were young even if it has newer sequels.
Despite having better sequels nostalgia always brings me back to Civ1, Heroes of Might & Magic 1, C&C1, Dune 2, Warcraft, Doom and plenty of other old games (RPGs etc) every decade and when I visit their communities to reminisce I always seem to find others doing the same. I think sometimes people crave the simplicity too as we're all busy in our 'old age' and playing a hardcore deep modernish 4X game after a long day at work can be not so great forcing you to leave it till the weekend, whereas an older simpler strategy game is not so bad on a weeknight when you're tired. Obviously there's a bunch of us here still enjoying, playing, talking about and modding Civ1 despite zero effort by the publisher to sell or market the game anymore so I'd love to see how many more would come if the games were on Steam & GoG.
Of course I know you'll probably say that Civ has superior sequels with better advancements than a lot of those other games I've mentioned, however part of the work I do here for CivFanatics has me sharing our front page news across all the big Civ groups out there with tens of thousands of members in them and so I regularly see what's going on in those groups and oh man.. not a month goes by that I don't someone posting screenshots of their latest Civ1 or Civ2 game and then you look in the comments and it's filled with people saying how much they've missed them or that they're still the best ones in the series resulting in lots of debates as every fan has their own different favourite iteration of course heh.
When you consider that other publishers made the effort to sell games from the friggin 80s that look even worse than Civ1 and entire companies out there survive on a business model that revolves around reselling old games (that in many cases look terrible lol) I'm sure Civ1 would sell enough to make the effort of them slapping it in dosbox worth it (as surely it wouldn't take them long to do it).. the sales won't be be anything amazing of course, but I think I'd be more than the next to none you're suggesting. Especially if mainstream media picked it up due to Steam and 2K posting news about it. However sadly we may never get to find out if I'm right as who knows if 2K will ever do anything sadly.. but I'll keep pestering them every year as I'd really love to see what would happen here in this community if they did something.