It sounds like you already have an II membership and your offer is to simply upgrade is from a regular to gold/platinum. Correct? It appears your "offer" is $5 off the gold upgrade fee. I would take a pass on it and only purchase it once you are ready to use it.
If so, then presently you have the ability to check out Getaway availability to get a handle on what is out there. This inventory can change daily, so best to maybe check it out for a month or so to get a good feeling of inventory that shows.
Short Stays are a feature of Gold.....but this is not a discounted getaway for you to purchase. You obtain these by depositing your week and getting 2 shorter stays vs 1 7 day. I don't believe it a feature used a lot because most of the inventory is just so-so.
Next time you log into II, check to see if you have any Accommodation Certificates (ACs) linked to your account. Go to Exchange, then my units, look for My certificates. If you have anything there, that is the place to play around looking for decent last minute availability. There are some real gems that can appear there and will cost you $300 or less to use one of the ACs to purchase.
Lastly, there is a section right her on Tug called "sightings" This is an area that other Tuggers post good things that they find on II (and RCI). A lot of last minute, nice resort availability is shown there. There is also an AC thread dedicated to "good stuff" that the ACs can pull. Consider joining TUG, by becoming a member, you will have access to this area.