DD just turned 5 and is about 35 lbs. We currently have 1 Britax Marathon (which she doesn't like - we use that as our spare for friends) and 4 Britax Roundabout 50s. The car seats don't expire until early and mid 2016. We have four cars that we need seats for...mine (Toyota Highlander that we use prob 90% of time, nanny's car, MILs car, and DHs car which is a 99 BMW with no latch that she is not in that often. We have a small convertible that he will usually drive if he knows he will not be driving DD that day). She still fits in the Roundabout 50s, but most of her friends switched to Boosters at 4 and I kept telling her we will discuss it when she turns 5. So, of course she brought it up. I cannot figure out what to get. A friend is selling us a Britax Frontier 85 for $100 (DOM 12/12). They only used it about 5 times and then it didn't fit right in their new car with 2 other carseats. I was thinking of buying her a new Britax Frontier 90 for my car. For the other cars and the spare I was thinking either the Graco Nautilus or Britax Parkway. I have not seen IRL, but in pictures the Graco Nautilus looks more like a carseat than a booster, and her male BF puts up a huge fight whenever he has to ride in a carseat in our car. If I got the Parkway for the spare for friends would you be against your 5 yo in a non-harnessed booster (I will keep one of the roundabouts as a spare too)? I prefer for DD to be in a harness for long trips where she may fall asleep, but I don't think I would be against her being in a Parkway when in a friends car. If I get a Parkway would you get the SG or SGL?
Also, if I were to sell the Roundabouts/Marathon locally what would be a fair price?