Thanks for the input everybody! I have other (smaller) backup machines that handle basic piecing just fine so I don't think I'd get as much value out of keeping the 6600 as a backup as I would if I traded it in or sold it. I don't quilt for a living so if I am unable to easily quilt a sandwich for a few weeks my world won't end. I figure if the dealer doesn't offer a good price I could just sell it on my own but I'd much rather trade it in.
My dealer has a really good reputation around here so I'm optimistic that they'll offer a good trade-in; I just wasn't sure what to expect.
KalamaQuilts - I can't say I've used ALL of the bells & whistles on the 6600 but I've used a LOT of them. I make a lot of quilts (18 in the last 11 months!) but I also make plushies, bags, various other projects (dog beds, curtains, hot drink cuffs, etc.) and general clothing mending/hemming, and am starting to get more into more advanced clothing alteration and will probably be diving into clothing construction soon. So I have even used quite a few of the "fancy" stitches - more than I thought I would, actually. I think the thing I use the least is the lettering stitches. Oh and the knee lift - can't get used to that.
The 3 main things I see on the 8900 that are making me want to upgrade are the free arm (I really miss that, more than I thought I would), the quick-change needle plate, and the extra 2" of throat space. I recently FMQ'd a king size quilt on the 6600 and would like a little more room to do more large quilts like that since we have a king size bed. It looks like on the 8900 I'll lose the ability to wind a bobbin while sewing though, and I'm not sure how I feel about that, that's one of the features I really like about the 6600 and I think I'd miss that. Also not sure how it holds cones - I like how they sit on the 6600 and would rather not deal with a separate cone holder if I can avoid it. The dealer opens in about an hour so I'll find all this stuff out soon, though.
