We have both a doorway jumper and a jumperoo and DS loves them both. Our's goes up to 25 lbs. I guess it depends on how close to walking your DD is. Is that when they lose interest? I'd rec. buying one used! I got our doorway one for $10 on craigslist and it is by far DS's favorite thing to do.
Now that DS crawls and can pull up to a stand he wants nothing to do with the jumperoo. Everytime I go to put him in it he starts crying. I guess it would depend on how mobile your LO is.
Re: Too old for a jumper?
Abbey still loves hers, but my SIL who has a dd 1 year older said that as soon as her dd could stand up, she didn't want to be stuck in place anymore.
That said, if you're planning on more kids someday, you could always look at it as an investment!