The stitch quality will most certainly be as beautiful as the 730. The 707 does not have quite as many stitch selections but I never use much other than a straight stitch, zig zag and occasionally the blanket stitch so just a few stitch selections would be just fine with me.
A common issue with the older Berninas (700s, 800s, 900s) is that there is a nylon (? or some kind of plastic) gear on top that cracks and causes the machine to stick at that point. Both my 830 and 730 needed this gear replaced when I bought them. I think the cost was about $70 to have it repaired by a professional. As long as the motor sounds good I would not let that deter me from buying your machine. Hopefully you can do a bit of stitching even with a cracked gear (if this machine has that issue) so you can see what a wonderful machine it is.
Let us know if you buy it!