Hoards are definitely a neat part of a lot of peoples' pet collections on CS. People certainly like to strive for or achieve a variety of things, like a complete pet collection, a complete item collection, their dream pets, etc., and hoards are just yet another of those things that can make people more eager to keep playing on CS. There's always two sides to the argument, but I still don't really see a problem with trading for pets one really likes (whether due to design, a personal meaning, something that is striking, etc.) to collect a bunch of them. Plus it gives us who need something to do... well, something to do!
What do you hoard?I have two hoards. Although the smaller of the two, my primary hoard is Sunbacks. My other hoard, though much larger, is the more "minor" one, and that's my purple sunbacks hoard (the ones from April Fools' 2013).
Why do you hoard them?The sunback is my favorite pet on the site. Originally, it was the moonswirl, but the sun design on the back of the sunback just fascinated and intrigued me, and over time I came to really love the design. The golden color and radiating nature in general is also just a major bonus.
The purple sunback hoard reasons are somewhat similar. The designs are very similar, so those are the same as the ones regarding the true sunbacks. However, purple is also my favorite color, and so the combination of my favorite pet with my favorite color just made me jump out of my seat, and I had to collect more of them.
How large is your hoard?My sunback hoard is currently at 12.

My purple sunback hoard is currently at 377.
What is your goal for the hoard?My sunback hoard doesn't have a goal or anything. It'd be nice to eventually get it to 20, although that would take a while. I'd also like to get them all decorated completely finally at some point as well. The purple sunback hoard does have a goal. Originally, I set it as 1000, but it turns out that the number that seem to be out there is fewer than I thought, and this is much more difficult than I expected. At the moment, I have my goal set at 500, but if / when I reach that, I will more than likely extend the goal to 1000, which will definitely be my stopping point.
Do you overpay for hoard pets/items?I do, for a significant amount of them. For my sunback hoard, I've paid at minimum fairly for them, and for some of them I have given slight overpay. As for the purple sunback hoard, I've overpaid for almost all of them. In terms of single swaps, I generally swap with a pet that's 4-5 months or older, and with larger quantities of trades, I've been giving older rares (like early-mid '09 rares for 20-25 of them at a time). If I really like a pet, I will definitely be willing to overpay for it, and that goes for both of my hoard pets.
What was the first pet/item in your hoard?For the sunbacks, the 9th sunback in my group (Sunny) was the first sunback I traded for. I think that first sunback really gave me the push and drive to keep going and possibly trade for more, which I subsequently did.
For the purple sunbacks, I'm pretty sure it was the one sitting in my April 2013 group at the moment. It was my first one, and I needed it to maintain my collection, and afterwards I just got the idea of hoarding them, and it blew up into the hoard I currently have.