I actually think the current system works pretty good.
We all sold jewels, or were close to, first rr, so that's a non issue
+zen on a main is going to be a waste if its +1% / +10% or even +50%, this is really only an alt farmer option.
The thing with +10% is its actually quite a lot. I have to use an example to prove my point.
Say you get 5k zen per drop, and you get 5 drops per minute. That's 25k zen per minute. You then take away your helper / pots cost per minute and lets just say for arguments sake you end up loosing 1k p/minute.
Then lets say you equip a +10%zen item. Now you get 5.5k per drop and 27.5k p/minute. Now you make 1.5k per minute. Another item +zen will put you at 30k p/minute (4k profit p/min), which is not just 10% more than you were getting with 1 item (1.5k > 4k = about +270% more)
Since the majority of the zen that drops is used in running the helper, any amount more is pure profit.
Combine this knowledge with having a look at the base zen drops in each map (monster level is only a small part of how much zen drops... each map has a different base there's a post from admin on this) and keeping in mind kills p/minute is just as important as exp per kill, and you can make decent zen. (My alt in full +zen set 6rr is making around 3kk zen p/hour)
Regards,
Enk