how would their project get maximum exposure without spamming social media
Not all project do that. In fact, they should never do that as it only causes potential investors to turn away. I think it's not effective either.
Depends on what their product is, signature campaign, content creation/translation and probably development bounty are better for them. I know two projects that instead of running a spam festival campaign, tried to engage with their community via various development and marketing bounty. By marketing, I mean connecting with potential clients directly and so on, instead of RT-ing their tweets.