I have grown to like a beige and tan Elna Supermatic a lot. I had to replace a drive pulley behind the hand wheel, and I was lucky to find a metal replacement with rubber O-rings. The particular machine I fixed up was very stained and oily and packed full of lint, it cleaned up very nicely. The reason the previous owner couldn't make it work was mostly because of needle was in the wrong way and for some reason it had class 15 bobbins which interfered with the bobbin tension. There are a few here who find them noisy and hard to repair, but mine was well withing a DIY fixup and it has behaved well since. For a domestic it's a fast machine, and I have to admit mine is a bit noisy when I floor the pedal, but mostly I go slow to medium to get the stitching right. If you need to stitch at 1500 stitches per minute for longer periods of time this is not the model to go for. 1000 stitches per minute is fine though.
Some times a model has been given bad review because owners haven't taken the time to sort things out or taken time to know the machine. Other times a model has it's limit and doesn't fit it's purpose.
The later Necchi models like Lydia were very nice models with stretchy stitch patterns, but some plastic parts are almost always cracked and it's not easy to find a way a good way about it. I don't think it's impossible, but it has to be a better quality replacement part than the original. The earlier Supernovas and BU models are very dependable and well behaved.
With models like Bernina a repair generally results in a very capable and durable machine, and is well worth the time and money it takes to repair them. Bernina kept their high standard from the 50s (before the war really) and up into the 80s. With other brands it can be harder to generalise.
These days many consider machines from the 70s and 80s vintage, and some models have more problems than others. Flimsy builds, low priced models aren't favorites to spend that much time on. On the other hand there are been a few surpises; a simple Taiwan built straight stitch - zigzagger model, very sturdy and all metal flatbed from 1970s. A girl bought it as a replacement for a misbehaving Brother model she had used for years. It turned to be the perfect replacement to sew anything from soft leather belts to applique on dog coats and accessories. Bargain priced Brother models have a bad reputation, but I guess it's very model specific. I don't think there are any comprehensive overview of them since there have been so many.