Recycle and reuse that old, worn out chain by cleaning it then looping a section of chain around the seat stays and through the saddle rails to prevent thefts of opportunity.
This isn't absolutely secure, but this prevents quick swipes, especially if you have a quick release seatpost binder. To do this, you need a chain tool to break and reconnect the chain links. Some bicycle multi tools come with a built in chain tool, or you can get a cheap tool for about $5 or something a little fancier for $13 and change (plus tax and shipping). You'll note that Ana also uses a couple of sections of inner tube to protect her bike's finish.
This is a good technique, but you should also consider not using a quick release on your post. As you say, a multitool is easy to carry, so if you really need to adjust it, use the multitool. Just don't leave it with your bike, and the same goes for your chain tool.
I got the idea from some picture I saw online, of some bike in the US. :-)
Yes, I know I should take off the quickrelease, but I haven't felt the need yet, I seldom leave my bike parked in the street, unattended.
Although I was aware of the more suitable set up for an Xtracycle being a hardtail, I gave it a try because a) they did mention some customers with full suspension bikes were happy with the set up, and b) that was the only bike I had and there was no budget for a new one. ;-)
But it turned out pretty good, actually. Of course, with a hardtail maybe my energy input on the bike would translate into movement more efficiently, but for the use I have been giving it it's just fine, really. And I have a very smooth ride everytime. :-)
My boyfriend has exactily the same set up, only his is a bigger size bike (mine is an M, 26'', his is a L, 28''). He has been finding that the rear suspension does steal some power out of his pedalling. Maybe that has to do with the fact of being a bigger bike, or him being heavier than me,... I don't know. When he installed the FR kits he adjusted the spring to its maximum "rigidity", but, surely, a new hardtail bike is in our dreams. ;-)
BTW, if you want to make your non-quick release connection secure, hot glue a BB (no, not a Blackberry) into the hole. When YOU need to make an adjustment, you just melt the glue. Until that time, someone can't just walk by with their own multi-tool and help themselves to your seat.