hazofhorsham has it essentially right. There is a point where you reach the goal and the profit margin is just right, and beyond that you can see a diminishing return because your margins start to drop as you increase shipping costs and "give away" more decks at a lower cost. It's all good in the end, as the project wouldn't have happened without Kickstarter, but when you calculate that all out, work in the fees, taxes and shipping plus all the production costs it's not like you are swimming in dough, even when you go way over the goal.
Setting up these projects is actually hugely complicated to do right. My wife and I spent hours working with the numbers in complicated spreadsheets trying to work out the exact mix of rewards, how many of each thing to offer, what "extra" costs there are for each, what the shipping estimates will be, how many actual packages need to be mailed, what the real cost per deck is as you sell fewer/more, how many decks will be left over for normal sale, what packages lose money, etc etc etc. I suppose you could run a KS project without all that, but it would be all to easy to get to the end of a successful project and then realize "Oh wait, I just got hosed".
Tendril will work out well in the end. We estimate that a bit more than half the total decks will be spoken for via KS, which will leave a fair amount to get to some resellers (mainly for the marketing exposure) and some for sale on my own website. That should fund deck #2. I will probably employ KS next time as well but at a much smaller goal and only as supplemental income, more or less. I've had a HUGE number of casual buyers come through Kickstarter and if we can reach a few more people that might not necessarily be card people, that is helpful.
Kickstarter is amazing because it allowed me to do this, but it surely adds a serious level of complexity if you aim to do it right.