In the past, we got discounts on Hoppers - we don't anymore (back when they were UPHs). In the past we COULDN'T get the dining plan (now we do). Way back in deep history we were eligible for maybe the Silver Plan or something. Dining discounts and perks come and go (and are fairly limited). So do member events and little perks. Sometimes there is more or less happening at the Community Halls. Pool hopping to SAB used to be available, now it isn't, and they could remove that perk entirely anytime.
The availability at seven months has - in the perception of some people - tightened for some of the resorts. The availability even ten or eleven months out has tightened for some rooms at some resorts.
Over the years, there have been changes to housekeeping (the first few years at OKW it was daily), in room linens, and some of the stuff in the room (like they added DVD players and wireless - which we had to pay for for a few years and should be free this Spring now that the equipment is paid off).
Big recent changes are the booking fee at Disney non-
DVC resorts and the banking change.
When I joined they had room assigners who assigned rooms in the order they were reserved. Book at eleven months, and you pretty much got what you requested. Then they got rid of the room assigners - for a bit BW wasn't a guarenteed category and BW owners had fits. So BW became a guarenteed category. The system then was "room ready" - the front desk CM put you in whatever room was clean and/or coming available that day - if it met your requests great - if it met someone else's requests - too bad, they didn't get there first. We seem to have gone back to pre-assigning, but as far as I can tell, it isn't the thoughtful assigning it was six years ago - the worst of both systems.
Disney has been making noise (some of it is Disney, some of it is just amplification of some people here's wishes) about commercial renting.
Trading options seem to get more expensive each year - and I get the feeling that they are also shrinking.
Read the contract and figure out if its a good deal for you based on what the contract promises you. Don't buy for perks or trading options. Buy to stay at your home resort. Buy knowing that a timeshare is "first come, first served" and there are not enough rooms for everyone over holidays - so you need to be able to plan ahead.