We went to Costa Rica last year, but did not stay in a timeshare. Its an absolutely amazing country to visit.
Unless you are planning to tag on a timeshare stay at the beginning or end of the visit, I would not recommend timeshare for Costa Rica. Distances are deceptive as driving times are usually much higher than similar distances in the US, and if you are going to Monteverde or Arenal volcano - getting to/from tires you out because of the dirt road!
We decided to rent a car and drive ourselves from Monteverde to the coast - wow, that was some experience! There is no road to speak of, and no road signs - on the other hand, you follow a dirt road, and any splits off the main road usually terminated after a few buildings, so you could get back on track. My 8 year old daughter sitting in the back seat called the experience getting a "Costa Rican roller coaster". Absolutely beautiful scenery, and in some spots you feel like the only people on earth! Kind of scary with two little ones in the back, but a great memory afterwards!
Anyway, can't help you with timeshare info, but just wanted to say good luck on your trip, and post a trip report! Awesome place to visit.
PS - the major highways between other places were fine, its only Arenal to Monteverde, and Monteverde to anywhere that has no roads.
