Using Gems to Boost Defense?

I feel that a lot of the focus of clash is on the offense ( you really don't get any loot reward for a defensive win - you just don't lose loot - I'll post about defensive win bonus another time)
Then I realized the reason behind this is that it's easier to spend money and gems on boosting offense - troops, spells, etc.
But to add a little more ways to spend money on this game - what about having the ability to gem your defense for a period of time so it was more powerful when people tried to attack it? For example for 5 gems your lvl2 xbow could be a lvl3 xbow for 24 hours or maybe longer. Or your lvl5 ad could be a lvl6 ad for 24 hours. Or 5 gems to boost all your walls a level for a certain amount of time. Would allow u to have a stronger defense and protect loot. Perhaps you could then even have a defense that is above your TH level for a short period of time. I'm not sure if you could allow this in war but in normal attacks it would work better.
It's gotta be a good idea if you have to spend gems/money, right?!