Its an interesting case, it really depends per game.
For Gen 2, I say yes. HGSS added SO MUCH and took away practically nothing. The only reason to go back to play GSC is if I'm feeling nostalgic for the sprites and art style, but even then, HGSS has all the original music with the GB Player! (Which I normally just Gameshark into the beginning of the game to toggle whenever I feel like)
For Gen 3, Emerald and ORAS each did amazing things, and its hard to tell which I like more. Emeralds rosters for the Gyms Leaders, Extra features like Safari Zone, Marine/Terra Cave, Both Evil Teams and of course the Battle Frontier make it one the best games, BUT the improvements to the Story, Characters, Graphics, Music, Modern Mechanics, etc. make it really hard to go back. (And hey, as much as I love the Battle Frontier, I doubt Im ever gonna raise a competive enough team in third gen to actually play it)
Gen 1 is gonna be interesting. FireRed and Leafgreen are my favorite games ever, but I'll admit the sprites and music are a little bland even compared to RSE, but it got so many things added to it like the Sevii Islands, thats not even a concern. I'm curious to see if Lets Go Pikachu and Eevee will manage to top it. I think the PoGo mechanics have potential to be fun, and I really dont mind the removal of things like Held Items or breeding (They were never really needed for Gen 1 or FRLG)
Little iffy on being locked to the fist 151 only, but I dont mind that nearly as much as others. A smaller roster will let Gamefreak give more attention to each mon and force them to get creative with Game Mechanics with them!
What does bother me is that they replaced Red and Blue as the PC and Rival. That simple story and character dynamic was one of my favorite parts of Gen 1, so I'm upset seeing it removed, but I trust Gamefreak knows what they're doing with their characters and have something special planned.
On the flipside, the new Kanto looks and sounds amazing! Overworld Pokemon make it much more alive and Mega Evolution is in! If they add in the Sevii Islands, or atleast some postgame island equivalent, and add in the only things Kanto was missing (A way to rematch Gym Leaders and a Battle Tower equivalent, preferably both in one like Gym Leader Castle or the Battle Tree) and if they really flesh out Kanto as much as they can, atleast to the equivalent of modern games,
I could see LGPE overtaking FRLG as my favorite games! (Maybe until Gen 8 comes along and blows me away too!)