Rate of juice gain is largely an issue of annoyance, and potentially danger of massive rap sheets if too slow. I don't think it really matters within reasonable limits.
The lower the ratio of juice gain to crime/heat incurred the higher the potential of persuasive Conservatives to disrupt your life. Losing 100 juice means a lot if it's 100 acts of treason to regain it. As long as there are relatively low 'scare'/heat crimes you can commit for juice however it doesn't really matter, except for annoyance reasons. I can mechanically go and rob the downtown apartments a hundred times for 1 juice apiece if necessary; it's only really a matter of sheer boredom (and, in that very extreme case, time - for most purposes even 20 site raids is inconsequential, let alone the 15 it currently takes to juice to full if you have good stealth skill - the cosmetic labs give massive juice).
From a balance point of view, anything in the reasonable range of juice rates is largely inconsequential. It only matters when you have extremely fast or slow rates. Only juice caps would really matter much. Not being able to simply steal or vandalise your way to Elite Liberal would make things much, much harder for my play-style. Having only the really ballsy actions (murder of elite Conservatives, treason, some other special site actions) available to juice to full would be an interesting change in my opinion.