The reasons why upgrading walls with elixir is a bad idea
I have the following reasons to say why it is such a bad idea for Supercell to introduce the option to upgrade walls with elixir:
1) Lots of people have agreed that after wall level 7,8, the walls are more a decoration than functional. It is quite often to find TH10 with maxed defense but maybe lv7 walls, and those bases are not much easier to attack than those with both maxed defenses and maxed walls. So, giving the option to expedite the wall building does not help player much.
2) There are lots of attack strategy that totally avoids walls. Even for ground attacks, people always talk about defense level and layout, but how often do people talk about wall layout? The level of walls and wall layout is probably the last thing to consider when attacking. So, giving the option to expedite the wall building does not help player much.
3) Besides the biggest lie "protect your town hall at all costs " which SC used to mislead lots of new players, now there is another big lie/temptation SC put there to lure them to invest valuable resources into the useless wall-building. This means, walls may divert resources from defenses, which is probably the worst thing a player can ever do. Not only does this delays the progress of defense, this also make those player stay at th7/8/9 longer, which makes them easier target for TH10 raids, which further delays their progress.
4) Nowadays, as long as you have at least one grill fired up, it is very unlikely that your storage will be raided. But, even as a maxed TH9, you can still expect lots of attacks from desperate TH10s for your resources.
So, it really makes no sense to upgrade those walls. Get to TH10 and fired up your grills, and you are untouchable.
Your Opinion is Duly noted
But there will be players who will disagree with you.
I personally need every drop to keep my army rolling right now, so I am fine using gold instead of life's blood of the armies!