For now I haven't used money to invest in any crypto......you know how volatile the system can be,so it's best to do so with money you can loose comfortably,at the moment I invest my time which is on airdrops and bounties.
I guess by spoofing number of upvotes to a question or answer makes it higher on the lists. That alone makes them more visible to people that also votes and then they generate revenue.
I have used and experimented with them many times before and they arent that helpful (maybe in the past they were), but now they are generally break even at best so not to helpful.
They might give you some extra eyes on your content by getting it to the hot or trending page (if you spend alot!), but your better of engaging with people and using the dapps to earn steem