The "secret" to using RCI, in my experience of over 9 years, is to request an exchange EARLY EARLY EARLY. Even then you **may** not get your requested vacation spot--it all depends on a number of factors (the date you request the exchange, the size unit you are trading, the "value" you are trading vs. what you are asking for, other requests that come into the system that have "priority" over yours. The only places I have trouble exchanging to (even with more than a years notice) is the Eastern seaboard beach-type places in the summer (Myrtle Beach --have never gotten in to; Ocean City MD had to downgrade my exchange to a studio unit--I traded in a RED, 2 bedroom sleep 8) I have *never* had a problem getting the Orlando area but sometimes you have to wait. I am not sure exactly what a Worldmark membership is, but if it is a vacation club (you didn't actually purchase a timeshare to use in exchange, you basically purchased "weeks") vs an actual timeshare I am not sure what "value" RCI puts on it (Red, White or Blue). When you own a timeshare your timeshare has a Red, White or Blue value based on the season which you bought your week in (i.e. all of Florida is RED, while January in a beach place like Ocean City is WHITE--the lowest "value")
RCI does not always have an exchange available as soon as you request it. If what you requested is not available, they put you into a sort of holding pattern (they call it a search) whereby their computers will spew forth information on a unit you requested when/IF it becomes available.
It is also best to request an area not a specific resort. Once you have your RCI member number, go to their website and look up the particular dates you want. You can also enter the resort ID if you want only a particular resort. Then you can play with your dates on the pc until you come up with something suitable. Once you get to the listing page of what is available for your specific request, click on the name of the resort and their directory listing will pop up. Always take a "Gold Crown" resort if one is available--these are "the best" RCI has to offer. I then CALL RCI instead of booking online---I firmly believe (although they deny it) that there are options available that do NOT show on the website search function).
Some resorts (including Vistana and the Westgate resorts) have a 1 in 4 or 1 in 3 limitation---you can only exchange there once every 4 or 3 years.
RCI will not begin a search until you pay the exchange fee (so you pay the exchange fee at the time of your request NOT when something becomes available.) If nothing ever becomes available they will apply that payment to another exchange requset or re-credit your credit card.
As far as specific requests go: depending on the resort you may already be pre-assigned a unit when your exchange is made. When you get your confirmation if a specific unit is listed then the resort WILL NOT change your unit--you get what was deposited back into the RCI bank by the owner. If the unit is not assigned on your confirmation you stand a better chance of making any special requests.
You may want to check out my thread from November/December about the experience my family had at Westgate Vacation Villas. While I had heard many great things about Westgate they couldn't PAY ME to stay there ever again. There is a bit about the conflict between RCI, II (Interval International--another timeshare co) and Westgate. link to thread
http://www.disboards.com/forums/showthread.php?s=&threadid=14259&highlight=Westgate
I will pop into the RCI website and use my user id to search availabilty for you. I don't understand why you can't if you have already joined---your should have been able to request a search IMMEDIATELY upon joining. I would call them back and ask again. Like any other place, not everyone is as knowledgable as the operator next to them--some are new, some have been around, some CARE and will look extra hard for you, some will just pop your info in and whatever the pc says is "it" for them. (Kinda like WDW CRO--LOL)
UPDATE: Just searched using my timeshare as the exchange value--NOTHING for the dates you are looking for. Playing with the dates there were several available in January 2002 and a few in Feb. 2002 (1 bedrooms with a Feb 24 checkin and 1 2 bedroom with a Feb 1 check in --the Feb 1 was Vistana, the other was another resort). Of course, your results MIGHT be different depending on the "value" of the resort/week you are exchanging.