As far as adding exp. to a lvl 10 rune goes, (and I am not certain on this), but I do not think that adding exp into it would get you more of a stat increase. I do kinda have to agree with Matt tho that there really isnt a reason to level down a rune. The ONLY reason I could think of would be to get a morale for Calvin in Cerb/Baal. That being said, 5 fragments is pretty cheap for a purple morale rune in rune temple, and could easily be leveled and kept on another hero until time to change form for these events. I do understand that buying an extra hero costs credits (which are hard to come by at points) but at some point this happens by design as you get a new hero you want to use in formation over one you currently have in. The rune slots on those heroes are already unlocked so when this happens it does give you extra holding room.
Now as far as odds in temple go. There could or could not be some sort of odds system in play (other than randomness). And I am sure we wont get any type of conformation from the devs one way or another as to if this is true or not. BUT I will say that I am only VIP lv2, and have had extremely great luck with runes. And it has stayed consistent throughout all of server 1 (since day 1). I have seen others not have such great luck. I have all yellow runes on all heroes and lv 10 vengeance on my Adamanti, and have extra heroes holding a bunch of yelows for me for later use once more rune slots unlock at lv 80, and it is nice to have the ability to change things around if needed for Heroic Realm bosses and Quest Bosses and having those extra heroes to hold the runes comes in handy. I have also seen several players on server 1 that were not VIP at all have complete yellow rune sets from winning cerb/baal final hits alot and farming other players in wilds frequently to get the coinage for said runes. There really is no way to tell if there is some sort of "teiring" going on as far as odds go for things like runes and hero card drop rates, but the extreme cases I've stated that some players have leads me to believe that it is just luck. If I am wrong then that's all fine and well, it's just my opinion.
As far as some sort of tool for advanced rune crafting/de-crafting, I'd not be against this, even tho personally I do not see a use for it. If anything it would just give more options as far as runes go and more user control. As long as it isn't made to where it is necessary to use, and implemented more over as a "feature" then I see no problem with it.
interesting thread for sure