I don't dabble too much in Sci-Fi modeling but I'll agree that the AMT Star Trek kits were pretty dire.
I think a lot of it had to do with AMT's styrene. I always tried to avoid their kits because of that, their styrene always seemed softer and melted too much when you put the cement to it. Not to mention the seam and detail misalignment issues that plagued most of the their Star Trek line of kits.
Their TNG Romulan Warbird was nasty and had quite a questionable parts breakdown.
What really bothered me was their Cardassian Galor class model from their DS9 kit series. Nothing worked on that kit! panel lines on the top and bottom halves were so misaligned that it looked like two different people were given two different diagrams to do each half. The whole kit felt like it was some sort of afterthought to the rest of the series.
It really was a shame because it was my favorite of the ship designs from the DS9 series and when I had it completed and I compered it to pictures and images of the ship on TV,the model looked dimensionally and proportionately quite off in several respects.
Moving beyond Star Trek; does anyone remember the short lived "SeaQuest DSV" series from the early 90s? It ran for three seasons but only the first season was worth anything.
Monogram had the license to make kits for the series.
Their SeaQuest submarine kit itself was pretty simplistic, but not bad.
However, there was a utility type submarine vehicle from the series (I don't remember it's exact name, but it was pretty much an underwater pick up truck) that they made a kit of that was god awful in every way.
It had sink marks on many key parts that were in such places on the parts that scratch building replacements was about all you could do. The vehicle had a mesh enclosed cargo box that Monogram supplied as four clear pieces with the mesh patterned engraved on it. Try masking and painting those parts and then getting them together without fogging the clear styrene. I gave up on that one!
I'd also include any Games Workshop styrene kit I've ever built. I know some will argue and say RPG kits aren't Sci-fi, but we'll just have to agree to disagree.
Anyway, any GW styrene kit I've ever tried has been horrifically overpriced for what you get in it. You get basic shapes with little detail and poor fit.
I include them because, for the price, there should be a sprue or two of customizing parts included to make the kits into respectable display models OOB if you please. Not just low detail RPG pieces.