You make a good point regarding the storage problems. I don't fully understand this issues to be honest, so I won't try to debate this :)
It is no solution but a short temporary fix to feel better.
The problem with the spam right now is that no one seem to have a perfect solution, which is why I support both bots who tries to make people aware of the spam (such as @pleasestop), and @steemcleaners and the other projects that downvote spam.
I support @steemcleaners as well, they do a great job both informing and reducing the spam.
Remains to see if @pleasestop manage to up his service to a level of wide acceptance. I think he might, but may be he need some helpers as this probably become too big a task for one man and a bot. The spam he aims to fight is also very much a newcomer situation, where you got few followers and try to get your footprint inside community many look for the easy solution of saying HI by commenting posts and ask for a follow or upvote.
Issues about storage mainly appears because we are decentralized to a degree, and copies of everything is stored in each node.