Well I think that FreeVerb running at 18% of CPU tells you that you can do a lot more if you want to. Like 120 biquads (87%) or 680 FIR taps (96%).
But writing good DSP code is not primarily about the performance of the platform but what you do with it. Consider all the famous digital reverbs from the 80s and 90s, the hardware they were running on was extremly limited.
I hear what you're saying though, you'd like more performance for your money than what you feel you get with the OWL. These days you can get a Raspberry Zero for $5 which has (on paper) more than 5 times the CPU and many times the memory. But what you get with the Zero is a low-powered linux computer on a board, whereas the OWL is a high-powered, fully integrated embedded audio platform. There are fundamental differences which are not just about how you configure the system. If you don't believe me, try to run FreeVerb on a RPi with less than 5mS latency - and listen to the drop outs.
The OWL is unique in that it allows you to write high performance DSP code in a standard programming language, even polyglot, with a fully open source toolchain. No assembly required, no expensive development kit. Compile it and you get a high quality, low latency audio effect that you can pop into your gig bag and take on stage without worries it might crash.
As for the quality of the patches in the library, I think we have some really brilliant contributions and many which are totally unique. It's true that they're not all great, and it can be difficult to sort the wheat from the chaff. It's on our todo-list to implement a recommendation system to make it easier to find the gems, but resources are short and we've not had the time yet. But it's coming! Meanwhile, for a good stereo verb, try out the JotReverb. For a great effect that you won't find on any other pedal, try the DroneBox. I'll publish the current list of factory patches somewhere, they're all good. And there's 40 of them.
If you want to have a go at porting zita reverb I'll happily test it for you. And regarding amp/cab models: have a look at the Guitarix project. Porting to OWL is trivial as it is written in FAUST.