Considering an exchange in RCI will set you back $300 on top of the week you trade, that extra vacation is a great deal. That is only about $350 for the underlying week, which has a maintenance fee in the $1000 range. Generally you can't rent from an owner for less than they paid for the week unless they are desperate, and it is well below what Sheraton charges direct (I have in the past bought a couple of extra nights from Sheraton). Current June rates for 1BR/2BR are $170/200 per night; you can find these discounted through wholesalers, but probably not down to $92/nt.
Actually, that puts the room in the range of what we pay for a Holiday Inn Express on the drive down to Florida, and you get a whole lot more at Vistana!
But, do your homework, you might be able to find another good timeshare property down there for a similar price, but as you mention, you'll likely burn a better part of a day swapping locations. The last time we did a resort swap from Silver Lake to Vistana, we were settled in and by the pool by around 2:00 pm, but we were lucky to get into our room early around noon.
If you do take the extra week, make sure the resort knows (Diamond Lane works for this too) to link the two reservations. As long as you are exchanging the same class of room (ie. not a 1BR and 2BR), they should be able to accommodate you staying in the same villa for the entire stay.