MP3's have no erolin device, hence cannot cast spells anyway :P
Also, MP3 is a stage where people want to advance asap. The fighting, upgrading, spell casting etc is all restricted. That's why most people don't stay MP3 for more than a month nowadays. Most of the "learning" takes place at MP4 (at MP3 you don't even have vics)
Lastly, shop already has requirements based on days, honor, loyalty, etc.
IMO, MP3 development would come from:
1) Bringing in more players (which can't be done yet, see this ---> http://magicduel.invisionzone.com/topic/16018-what-happened-to-magicduel/?p=159281)... because most of the learning-things in MP3 are fun when done together with other MP3's
2) Better tutorial (already in progress)
It will not come from making changes to the shop, spells, trading, etc.
The MP3's system was always intended to be active apparently (constant arrival of newcomers) but since it is not so... maybe we can indeed have a few NPC's?