I haev the 7 qt, an upgrade from a 5 qt lift, that I purchased about 18 or so years ago. Do't even go to the 6 if you are thinking of upgrading.
KA sells refurbished ones on Amazon, and in the outlet section of their website. They also sell them through a store called Kitchen Collection. Most of the time, they are ones that have been used on photo shoots, per a KA rep I met in a department store. THe rep had also advised me to ignore the original pasta plates, an add on to the meat grinder, as something that would burn up your mixer.
.
Also, bowls and other things can be purchased through searspartsdirect.com, for less money than anywhere else.
I LOVE LOVE LOVE LOVE the 7 qt. I had a Kitchen Aid rep tell me to ignore the pasta extruder, as it could purn out the motor, but with this one, I have no worries. It handles 10 lbs of mashed potatoes during the holidays, cookie dough, and anything else.
I burned up one 5 quart lift, the top of its line at the time, making cinnamon rolls, so I've never done dough, but the 7 seems to handle it without ever getting warm.
Also, despite what KitchenAid claims, your mixer does not have to be EVERYTHING. Remember that when you look at the attachments.
Also, you need two pasta machines to not have a meltdown. You need to run dough through the roller, then move to another machine, or change the attachment, to make whatever noodle size you want, which is frustrating. And, why I'm keeping my 5 qt. Also, size matters. The ice cream attachment for the 7 qt is 2 quarts, and a different shape from the 5 qt. The water bath does not fit the 7 qt.
In the end, it depends on how much it is used. Mine, boith now, sit on my very limited condo counter, and the hand mixer I got at the same time has never left the box. My sister doesn't like things on her counter, and her HA stand mixer is still in the box. If it isn't convenient, you will not use it.
If you are thinking upgrade, skip the 6, and get a refurbished 7. Frankly, I'd start out with a 7 if you are thinking about one. It is better to grow into one than to outgrow one.