Buckeye Fan said:
I'm not familiar with II ... but it sounds as if it's more of a 3rd party that allows timeshare owners to deposit and trade with other owners?
You are on track! (Yes)
Buckeye Fan said:
What's the difference between a corporate membership versus a direct membership?
Dean covered this well above. With a direct membership, I have my
own relationship with RCI/II and may access their inventory by phone or website w/out having to go through my timeshare's Member Services desk. I also have access to their travel planning services (flights, cruises, hotel, car, activity reservations) and discounted rental weeks.
I pay an annual membership fee to each exchange company -- but may link several timeshares to the account. One membership fee to II covers both my Worldmark and Warner Springs Ranch exchanges. One fee to RCI covers Worldmark, Grand Pacific Palisades and my South Africa week. I can trade anytime day or night through their websites and enjoy "hunting" for great trades using their search tools. (My personal goal is to generally book any given reservation with the least expensive tool. This morning I found a 2BR week spanning Memorial Day 2009 along the San Diego coast using my Grand Pacific 1BR unit. I searched again using my South Africa week and put it on hold using the less expensive trader.)
Buckeye Fan said:
Aside from lower MFs, why would a membership through another timshare be better or offer more trading power than DVC?
Aside from MF and trading -- the real reasons I might find "another timeshare to be better ... than DVC" include
location (I'm in San Diego and often travel in the western states), and owner perks: day-use, bonus time, etc. What is better for me may not be better for you. Warner Springs Ranch is a perfect example -- it is 90 minutes drive from my primary home, allows day-use access to the hot springs pool, free golf and free equestrian to qualified owners, etc. This is
ideal for me -- but what good does day-use offer to someone more than 125 miles away?
Related to trading, I tried to hit the
first part of the question in my examples earlier. Recap: GPP offers bonus weeks with each deposit (2 weeks of vacation for every 1 deposited) and helps me defeat a trading block covering a large number of SoCAL resorts; Worldmark allows discounted trades nearer to travel dates; Warner Springs Ranch allows me 24 deposits each year without increasing my ownership.
As for the trade power question ... I find that each of my properties has different trade characteristics. One matches to (exclusively) better quality resorts, another finds a broader range of locations. DVC limits the my destination options to a small subset of II's list of affiliated resorts. While these resorts tend to be very nice -- I'm very happy staying at resorts that have not made DVC's cut or might trade through a different exchange company. I need a
different timeshare tool to match to the inventory outside DVC's handpicked locations and outside II.
DVC isn't alone in this. When searching II using both Worldmark and Warner Springs Ranch -- Worlmark will find
fewer resort options than Warner Springs Ranch for most searches as Worldmark filters out the "lesser quality" locations. On the other hand, Worldmark can pull DVC and the Ranch will never do that.

So "trade power" is an interesting question -- and often w/out a single, clearly identified winner. Following Dean's car analogy above, we own different types of vehicles for different purposes: the 4x4 for exploring the backcountry, the truck for hauling fill dirt, the leather-seated luxury car for transporting passengers in comfort and style. Different cars for different jobs ... same with timeshare.