I haven't hit my cap yet, but based on my plans I'll have exactly 8. Knowing me, I won't be happy with how everything turns out and I'll definitely end up needing more. Bridges, too.
My current town plan uses six inclines and six bridges. But that’s without terraforming, and I took the limit into account when planning, so there are a few spots where having the option to build more inclines and bridges would be nice.