I have had an account for years. I recently have been on it a little more, almost entirely because car friends keep showing me cars they have found for sale on Marketplace and I was sucked in.
Some say Marketplace is a better place to buy and sell than Craigslist, but so far I have found the sellers to be every bit as unresponsive and likely to get peeved at you for asking if something is still available (because they sold it two weeks ago, and you should know that even though the ad is still up).
If anything the people selling old cars I am interested seem less knowledgeable and informed, often selling for an elderly relative or something. Search engine is not so good either.
I made the mistake of joining a couple car groups, not near as knowledgeable or useful as anything I get here or on the team.net email lists.
But it is better than Pinterest, which as far as I can tell was primarily designed to clog search results.