I don't know sewing machines- but have you done a search on top-rated, etc machines? I know it's way different, but that's the way I picked out my vacuum cleaner (which I am IN LOVE with), and now I do that with every big purchase I make.
It may even help to go to the manufacturers websites and see if there aren't reviews online from people who have purchased that particular model, for instance. People are sometimes partial to their own machines, so it may be better to seek out a site like I mentioned above. ? The thing is that a manufacturer may say- model ABC is the best, but if all the reviews say otherwise, well there you go. At least it's better than nothing.
As far as a machine specific to what she does??? Maybe you can set up your sister or daughter or something to grill your wife about what she thinks is good (as if they were going to take up quilting??? however you do it) about her machine and what she wants in a new one. Then they can relay that information to you. :)
That may or not help, but that's all I can think of- you are so sweet to take the time to search out a forum and think of getting your wife something that will mean so much to her!
Good luck- I hope you get more good ideas from the many experienced quilters on here!