I just priced this for the same trip I'm planning now and it is not a better deal than just booking my flights and car myself. (you can combine package elements - doesn't have to include hotel)
I had already priced airfare for 3 at $758, and the vacation quote for airfare (with one person free!) AND an economy size car was $955. Clearly the vacations are not using web only, wanna get away fares. This obviously doesn't include the "play free" option of saving money on the passes - which might make the overall deal better. But for the flights, it isn't the way to go IMO.
Also, if you book a Southwest Vacation, you get paper tickets, meaning you are not eligible to check in online 24 hours in advance. You can only check in at the airport.