First of all you can quilt on most any machine. You don't need a special machine. I love my Featherweight for piecing and I have a walking foot for it and have quilted lap size quilts and smaller on it. I have a 37 year old Viking that has been my primary machine until recently. That machine has sewn so many miles over the years and it was having some issues where getting replacement parts was an issue that I decided to get a new machine. I did get a Janome 8900qcp with the large throat. That has some nice features in addition to the larger throat/harp area such as needle down, thread cutter however if you don't sew or quilt a lot I'm not sure it would be worth the investment.
If I was just beginning quilting I would use the machine I already have if it is in good working order. Forgo the king size quilts for the quilting part or do quilt as you go method. Make smaller projects and have some fun. See if you really enjoy quilting before investing in a newer expensive machine.