I've never owned a brother machine, but a couple of my customers bought them from WM and were most unhappy with them. For me the answer is to look at a few machines including trade ins of the various top machines like elna, bernina, and factor in the cost of walking foot, zipper foot if they don't have them. Talk to a couple of repair men and get their point of view of fixing up the existing machine with the feet she wants - don't talk to them about trading it in. They will be figuring in their heads the value of it to themselves to resell and if it's a good machine they will talk it down. About 15 years ago I had my elna super cleaned it was a '74 and I paid $600 for it new. Service man offered me 600 for it in trade. I saw later that my friend had traded hers in and he was selling hers for $800. They were identical machines so I figure he saw a good deal coming his way. Profit on the new sale/profit on the trade in. I'm still using that '74 for most of my everyday sewing and piecing and frankly prefer it over my Viking D1. Quality is very important and the plastic parts of the new machines doesn't always make for a sturdier, quieter machine.
I always keep my existing machine, buy new and hand the old machine down to another as was mentioned in an earlier post. I do keep certain machines for my use. One for heavy duty, one for fancy embroidery, one for everyday sewing. To me the walking foot can make or break a purchase when the person wants to quilt.