I would like to simplify your recommendations a bit based on many timeshare experiences in Mexico and elsewhere( including the dreaded Grand Mayan ones).
First, recognize that all timeshare sales people have a fundamental problem; they are selling a product that has very little value for a big price. If you don't know that or know what you can buy the same unit on the resale market, then don't go to any timeshare presentation.
Second, your current timeshare has very little value - most likely none at all. If you are not aware of that fact, don't go to any timeshare sales presentation as they will prey on your ignorance.
Third, I agree with you here, don't go to any sales anywhere without your own mode of transportation.
Fourth, The contract rules (not words) in any business transaction anywhere in the world. If you don't understand that, then don't go to any business transactional meeting. Believing a sales person that they will guarantee something that is not written in the contract is as much on you as on them. Shame on them for lying; shame on you for believing.
fifth, if you do go to the presentation, remember you are in complete control for five days. What they put in the contract is binding on them - not you. You are free to change, negotiate, and rescind during that time - BUT YOU HAVE TO BE WILLING TO READ THE CONTRACT AND ACT.
The bottom line: knowledge will always defeat timeshare sales people. If you are not willing to learn and use it, stay away.