Thats actually a really good way of looking at it.
For me, the thrill came from the strategy of building a team, where you can plan out a tight strategy that you can use.
For me, adding new pokemon takes this away.
Its why I really likes HGSS. All of the pokemon where ones that I recognized, and so it was more about hunting down specific ones I wanted for my team, and knowing the strengths and weaknesses of every single 'mon. It comes from playing R/B/Y - you could easily pour over guides of each pokemon, until you knew all 151, and their strengths/weaknesses off by heart. you can't do that with 700 pokemon.
For me, 700 is more than enough. now take us back to basics, and explore pokemon who have simply been throwaway in the past, and had no significance even in the anime/spin-offs. I want less new creatures, more new regions. Lets have the biggest region yet, with access to past ones. Sod it, lets have all 5 regions. Let us go on a quest, and catch all 700.
Its a matter of preference. I'm not being a troll, or hating on the franchise - I'll still play X/Y. I just think that Pokemon could continue to develop as a franchise in much stronger ways.
you must have felt terrible when gold and silver offered up a real counter to mewtwos "i just destroy everything" tactic.
you can easily do that with 700 pokemon. mainly because you really just need to think about final evolutions anyway. that is sure to cut down the numbers to 400 or less. in addition to useless pokemon, like mr mime or magmorta, there has always only been about 200 pokemon you'd need to know.
most new pokemon are just like old pokemon anyway. like chimchar. its the torchik that does it right. its fast and strong, instead of weak and slow.
as for ingame, you never needed more than typing anyway. maybe ability now and then, but typing really is the most important. and thats usually given away by appearance alone.
also, what do you mean by explore pokemon who have been throwaway? unless they make a region of only zubat and pidgey, both will always remain throwaway. and theres not much to explore besides collecting all the different pokedex entries either together.
new pokemon, as well as new regions, are the basics for this game. exploring the new type combinations, the new strenghts and weaknesses, thats what made these games big. if you stop adding new pokemon and just have people run around new areas to catch them over and over, the franchise will die. imagine in heart gold and soul silver, they wouldn't have added the new pokemon at all. imagine it would have been just 251 and not a single pokemon more. only a handful of nostalgics would not have been angry to no end.
i agree that there are some points where these games could improve, but that would have to be in addition to new regions and pokemon.
people are pissed when they get new regions and new pokemon but pretty much the same old storyline.
they are pissed when they get a rather new storyline but have to play it in the same region with the same pokemon (just imagine the outcry if they would have made it like in black and white 1 again, only new pokemon until you get the national dex.)
people want all of that new.
so make it new pokemon, new graphics, new world (yes, world, not region, i agree with that, make it bigger) and then add some more. why not be able to start the game from different towns? so you meet different pokemon early on.
just check out a few other games. would you want to play 9 dragon quest games when they always have the same enemies? and those games are a lot more driven by story than pokemon. same goes for final fantasy. while everyone likes to finally meet a behemoth or bahamut, they'd feel quite ripped off if it was always just the same enemies with a slightly different story. or the same characters. noone wants another story about freaking lightning!
do you really want to use the same tactics over and over? because thats how it will end up without new pokemon. at least until they get one of each type combination for each basic role (like tank, phys and special sweeper, spinner, weather set up, spiker, etc etc). only when they made it that far, they have a legitimate reason to stop. cause then they really only could copy pokemon with new designs. and even that isnt such a bad thing. by all means, garchomp really is the better flygon. and infernape is just better than blaziken could ever hope to be. even with its hardly available dream world ability speed boost.
do you want to overcome the same obstacles in the same way over and over?
no matter how you look at it, new pokemon, besides completely overhauling old pokemon (which is not going to happen) is the only way to go. in addition to making everything else better at the same time