I've thought about this... The basic problem is: new players get pounded by veterans, they get out of balance, they get stat loss, hence they spend most of the time in sanctuaries, and almost never go idle, thus creating an illusion of not having enough mp5s to train with... Hell, even people to talk with...
I'd suggest a few possible solutions (if someone already suggested these things, I'm sorry):
a) Get rid of the stat loss, instead implement a stat cap, or a monthly stat decay if you don't fight. (maybe combined with the forced advance after a certain ammount of stats are gained)
b) A transit level between mp4 and mp5, where lowering exp is possible, but much less then on mp5 (like 5-10%), or maybe implement this on mp4... This wouldn't get more people to mp5, but would make those who make it to mp5 strong enough to stand up to the vets without the need of dipping into the WP shop to reset their exp... Would lower the ammount of strong mp3s as well, but would be a problem since there would be a lot of strong mp4s going around... But I think it could be tweaked so that it works better than the current system. Could be done by implementing a forced advance after a certain ammount of stats are gained.
c) Since there is already the 15 credits when your "recruit" reaches mp5, there could also be a 10-15 credits when you reach mp5... Even better, once you reach mp5, you get the avatar feature enabled without the need to buy it in the shop. Lower the gold-avatar quality bar, put the gold avatars lower in the shop, make the best avatars into red-gold avatars... or different colors depending on the theme of the avy, and put that in the place where the gold avys are now. Also, could be good if there was a creature somewhere in there to assure more shop action in that branch...
d) Something similar to something already suggested: Pick your inner magic doc when you reach mp5... (since there is no distributing of them at the moment afaik) Choice between 4-5 lvl one docs would be appropriate. Yes, this would eliminate the special feel and rarity of them, but still... In a community this small nothing is that rare any more... And besides, with most vets having 4 to 5 inner docs to their name, they still stay "special", especially the higher level ones.
e) A combination of the above.