I guess it depends what all you do for cardio. I didn't have a bike, but when Cathe announced there was going to be a spin workout with LIS, I had to have one. (And I'm not the only one out there!). Anyway, sold my treadmill for a spin bike and I really love it! I was never much of a runner, but with the spin bike I'm able to get a "blast" n another way that is also low impact.
If you have a gym near you, it might be worth taking a spin class or 2 to see if you like it.
Lisa