So...
Kensley has 1 booster seat, basically permanently fixed in my car (it's a given it stays there). We have Kellen's (used to be Kensley's) Evenflo Triumph in my car (love it WAAAY more than the new Britax or anything else!)
In the shared van we have a crappy (as in I don't like it, not as in safety) Safety First carseat that doubles as a booster for Kensley and for Kellen, the Britax.
Baby will probably be in our pumpkin seat for at least a year, as it's good through 32" and 35# and I doubt she'll hit that before a year

Kellen didn't!
So... In a year or slightly longer... what will I need? Another booster for Kensley, moving baby to the Evenflow and Kellen to the Britax? Another booster for Kensley for the shared vehicle (whatever it is) AND another Evenflo Triumph for baby?
I'm lazy and do not want to have to move carseats around, so we are more than willing to buy something else for the "other" car. I think the Evenflo Triumph we have will be good for another 2 or 3 years (I have to check the date), along with the "cheapy" that's all right (Safety First). Those may be something to consider, too.
Good Lord!