When sending coins through the post, may I caution you to always use a tracked postal service. Not withstanding the cost of such a service, which I appreciate is often an incentive to ignore this advice.
If you send coins through the post, and the packet is lost or stolen in transit, the best outcome you may hope for is disappointment and irritation on the part of the recipient; a far worse outcome is when the intended recipient labels you a liar, a cheat or a thief. In these circumstances proof of posting will not defend you; nor shall a reputation built upon here-say. A tracked postal service however, shall enable the recipient to know at what point the loss occurred, and while it shall not ease their disappointment, it shall at least defend your honour.
Similarly, a tracked postal service defends the sender against dishonest recipients - admittedly this is chiefly an issue when selling goods, and is less a problem when swapping or exchanging them. None-the-less, it is worth mentioning that there are a lot of thieves in cyber-space who shall claim not to have received goods - when in fact they have, and should you have received payment from them for said goods, demand a refund. Without sending the goods with a tracked postal service you shall not be able to prove receipt of the goods.
With the value of most swaps seeming to be relatively low, sending registered mail seems a waste of money, I've never had any issues with letters going missing.
Of course if your coins are worth big money then by all means send registered mail. But for low value swaps it's just not worth the while.
All registered has done for me is let me know that my package is in limbo. I've had one in Brazilian customs since February. I opened a case and still nothing but thank god for the registration number since evidently there's nothing else they can do. At 12$ for registered on top of the 9.50 postage to Europe it's not even logical to swap. An even exchange costs me way more than my swap partner... So it isn't really even anyway.