Thanks Mark, for confirming the name of the "thing".
And thanks, lagartija, for your ideas. Actually, most pieces I play and practice are studies and based on, or even exclusively consist of, arpeggios. (Examples at different levels: Sor Op31 #6 and Op35 #22; Guiliani Op 48 #5; Villa Lobos Etude 1)
There too, my main problem is getting to speed. Most of those studies are supposed to be played allegro, but in my hands they remain andante at best ... and usually for a long time larghetto or even largho.
My issues with arpeggios and arpeggiated chords may be related. Still, I'm not sure that resolving one solves the other, too. Playing a whole piece of arpeggios means sustaining the speed for a long time - which is part of my issue there (and not my main question here). Playing an arpeggiated chord, on the other hand, usually occurs only at brief moments during or at the end of a piece.
While still struggling with both, my impression is that the specific challenges are different. To play arpeggiated chords, it seems that my right hand needs to be in a momentary state of tension and relaxation at the same time. From other experiences (e.g., dancing Argentine tango or pronouncing a rolled "r") I know that it can come with practice. Just "how" is the question.
Continuing to practice "normal" arpeggios may be part of the solution. But it still seems to me that something else is required for those light gentle "rolled" arpeggios ... and I keep wondering how to practice exactly that.
Or am I fundamentally mistaken somewhere ...?