As an avowed offsiter how about a few "pros" for the offsite (full disclosure; we own 3 weeks at 2 different Orlando timeshares).
Space: an offsite 2 bedroom villa is much larger than anything you are considering. FW Cabins are 504 sf, AS Family Suite is 520 sf. A typical Villa at a resort is about 1500 sf.
Price: you have posted rates for on-site. Current rates for decent offsite villas run a bit over $100/per night (January dates, pulled from a recent post on the Orlando Attractions and Accommodations thread). About half or less. Pays for a lot of rental car (figure under $20/day for a mid-size car on Priceline, sometimes well under). If you book places like Vistana through a travel service, you are still getting hotel service; full daily cleaning. Renting timeshares from an owner is a bit cheaper, but generally only includes a mid-week tidy and towels. Rental homes are an even better deal for the space, but there is often a bit more housekeeping that you are expected to do (cleaning and laundry before you leave).
Convenience: a villa usually has a full kitchen and laundry. That was what got us offsite in the first place. My DS has a severe food allergy and is petrified of eating out after some bad restaurant experiences. I understand that Disney takes a lot of care in food prep; but I can't convince him enough to eat out. So we NEEDED the kitchen! But when we realized how much we save by preparing our own meals, well it became a no brainer. We tend to eat a lot more prepared foods for the week, so it's not really cooking; but it is very convenient and a huge savings. Also a quick load or two of laundry mid-week makes packing much lighter; Canadians usually fly in, so weight can be an issue.
The biggest cons - no buses to the parks (but no waiting for buses), no delivery to your room, no
Disney Dining Plan (but you can still eat at Disney and make reservations) and no Disney theming. Countering that - our resort has 7 swimming pools, 12 tennis courts, mini-golf, and lots of activities. I don't think that my kids are missing much, and they LOVE the space and privacy they get in the bigger space. Also, there are some excellent restaurants outside Disney that don't require ressies 5 months in advance.
I just got the latest PIN code offer from Disney and did a quick comparison. To get a similar sized unit (1500 sf/ sleeps 8) to what we own would quadruple our price over our annual fees. A few people have pointed out that there are cheaper ways to get that unit than through Disney @ 40% off, but even if I could get down to only triple the cost, I figure that staying offsite I can rent a car, pay for parking, and probably hire some personal services to replace those things we don't get and still have a chunk of change!!!
Whatever you decide, I am sure that you will have the time of your lives!