I say there should be no bg limit. It should be a MINIMUM of 30 runes. You should be able to add more as long as it is an EVEN amount of runes (Because of split BGs). If you add more runes good for you. It does come at a price. You see, higher amount of runes means less chance of drawing what you need at the right time. IT does allow you to use all runes you think may be useful but because of the amount of rune you have it lower your chances of drawing those runes.
No, I like having lots and lots of little screws to turn. Of course iti s up to the designers to find a reasonable balance between complexity and comprehensibility.