Back in the 90's I lived in Pittsburgh, and there was a local Pittsburgh talk show host who used to totally make fun of Star Trek as being about guys in lizard suits. Used to annoy the crap out of me, but your post is making me realize why. He just wasn't willing to go along with it and have fun! He was caught up in the poor special effects (although the Gorn scared me as a kid) and couldn't just get past that and have fun.
When somebody's got the mic, they're going to say stupid shite like that, because being "loud" supposedly makes them "right." But the fact is, also, that even now, TOS (and STAR TREK in general, maybe) is perceived as being mostly "for kids." And there's something to that, because so many of us first discovered the franchise as kids. Maybe we tuned-in on our own, or a friend showed us, or our family was into it ... whatever it was, kids were there, hiding behind the sofa when the Gorn was on, or the Salt Creature, or take your pick. And kids' fare, for the most part, isn't treated with much respect by anyone not a kid. Part of it being that when we grow up, we look back on some of the shite we liked as kids and we're like ... "woe! How can I have been a fan of this garbage? It sucks!!!" And part of it, of course, is STAR TREK has always been a magnet for social outcasts of one sort or another ... particularly nerds and geeks.
Now, of course, it's found greater acceptance but the dweebs never left. So, between all of this and the budgetary limitations of TOS, in particular AND its age (!!!), it's kind of an open target. At the same time, if you've enjoyed STAR TREK as a kid, it's one of those things where as you grow up, it doesn't stay in its "kiddy category," because you realise that it was "about" something, it was attempting to take on mature subject matter that, perhaps, you didn't clue in on, before. And that's a rare thing, especially in entertainment ... to be fond of something as a kid that holds up for you, as an adult. And you get to appreciate it on different levels, like as I say, live theatre and so on. That doesn't mean you don't see the cheesiness of the Gorn suit, or the Horta, of course ... but nostalgia alone isn't what's supporting it, as an adult. It's the fact that it didn't talk down to its audience and accepted that they were smarter than television usually assumed them to be.