If you want a copyright SUIT...then you need a registered copyright. You have the right to claim copyright to any work immediately that is on/in a tangible medium....BUT you can not file suit against another party until you take steps to register. There are 2 legal viewpoints on this. One says that registration must be complete and the other that only application needs be filed. No decisive court opinion has thwarted the other as yet so jurisdiction is HIGHLY important. Technically DMCA violations can't go to court for a copyright suit UNTIL the prerequisites are met. By that time, time deadlines may have been blown as the government is sloooow as Christmas.
Now granted, if you steal an image of some 16 year old artist's website and they send you a DMCA notice...you can bet that you can pretty much wipe your azz with it. BUT, governed by my "Don't be a Dick" policy, I would hope that you'd simply honor the request and remove the illgotten media from your site, there are no shortage of undefendable images out there to take.
The Poor Man's Copyright is not completely invalid tho, it's just not a copyright defense. What I mean is that it is still useful supporting evidence if your case is that another wrongfully filed copyright i.e. STOLE your property. But this is only supporting evidence and the burdon of proof that a theft occurred is solely upon your shoulders. But an officially dated hermetically sealed envelope will still prove that an item or work was in your presence on a given date. Should there copyright be upheld, it is arguable that that same envelope will evidence possession of proprietary information or ideas of "THEIRS".
But, contrary to popular myth, this Ghetto Copyright is not the same as (for instance) fighting a time barred debt where you as the debtor literally only have to site the statue of limitations for an immediate dismissal....if you show up with your envelope as your sole defense it will not be admitted into evidence and you will lose your case. Ghetto is only good if you're a drug dealer or a rap star, other than that the term still refers to CRAP...and if you intend to use a Ghetto Copyright as "proof of ownership/creation" than that's effectively what you have....CRAP.
Congrats on settling out of court, but I fear that your (Gas $$$) reference may be all too true and to the point as all the opposing parties were avoiding was the probable $10,000 it would take to enter a court room...even if they had a solid case or defense against you. The fact that you settled out of court DOES NOT denote that you have a significantly shored up or even defend-able legal position... only that those against you backed down.