If you could narrow it down to your price range and the features you are looking for (e.g., needle down, embroidery stitches, auto needle threader, thread cutter, etc.), you could get better recommendations of machines to look at. Based only on what you posted originally, I would suggest looking at used Berninas. Some of the older models, such as the 830, are workhorses likely to last forever. Better machines like this have the power to sew upholstery materials, etc. too.
If you are looking for a newer machine, new or used, I suggest checking the reviews at
http://www.patternreview.com before actually buying anything you find. You get to see the older reviews if you join, and joining is free. The reviews are very honest about pros and cons of machines. Your biggest issue will be that many reviewers don't test out a machine for years before posting about it, and one of your concerns is with longevity.
If you have been purchasing lower-end models, then you may find that mid-range or higher models in the same brand lines will be fine for you. I can't imagine one of those konking out after a few years of piecing and a few sets of curtains......