Yes
Choosing between base and add-on isn’t always straightforward. There are some obvious use-cases for add-ons with Ample: Capo force (Pos 1-16 in the expression map), e.g. You can play sustain, dampened, legato etc in any position on the neck. Others (not Ample-specific) aren’t so easy to decide: Trill (ht/wt) e.g., I’ve used both in different expression maps, but I’ve settled on Add-on for my Eastwest template. Noteperformer uses add-ons for things like staccato and marcato if I remember correctly, which I don’t. Basically, anywhere you find yourself creating base techniques for:
(A) (A + B) (A + C) (A +D) etc. technique A could probably be an add-on.
Toggles like capo mode, strummer mode etc. I have in the Init section of the expression map. For strummer, C#6=127 and for non-strummer instances C#6=1. I don’t switch between capo modes so I’ve never thought about it. I have B6=127 in the Init section of my expression map because capo force chord mode constrains me to write like it were an actual guitar and notate the positions properly.
FX for Ample is also a good use-case for an add-ons, sure. I don’t use them though, and usually just turn the FX fader all the way down.