I know full well at my next test level of 26 that my facets would be awful. Realistically it seems anything after 15 and you're gonna be FS weak. Regardless I will still be tested. Both to have more options for things to do in hyper (or just while cruising across a slab while waiting for build approvals more likely) but also just cause I want a lightsaber :) Free healing is always nice too.
“(1) For example, if someone has level 5 force detect, can they detect FS in a player after level 26, or 31?
(2) Are FS facets so low after a level that its basically not worth having them?”
The first question is answered already.
The second question - Ellias mentioned about XP. There is much more than XP. I.e possibility of creating lightsabre (when the quest will be implemented). Even on the lowest level some facets can be tiny but nice addition to your combat skills. And finally - RPG! you can play lame FS!