You're right Ashley...plastic has it's place. I use my Janome for applique, and for a few of the decorative stitches. I mostly use it because it was a birthday gift from the spousal unit, and I wouldn't hurt his feelings for the world and everything in it!
When it comes to straight stitch sewing tho, I head straight for one of the old girls. Anything that has the capabilities of zigzag or decorative stitches also has the capabilities of throwing a stitch or two to the side when sewing over a bulky seam. It's also more likely to break something if I ask too much of it, which I often do. Most of the parts that you can get for the "new" machines will also fit these old girls, unless you have a "other than side clamp".
As for the speed issue, all of my vintage machines have variable speed, controlled by how heavy your foot is!
And then there's the nostalgia thing. Seems that it becomes more important as we get older... there's just something kind of soothing about sewing with an old machine, be it electric or treadle, when you think about the prior owners and how proud they must have been of their "new, modern machines".