There are a number of factors.
Let's start with one of them. When you were a kid, did you ever mix vinegar with baking soda? Remember the bubbles? Those bubbles were filled with carbon-dioxide gas released from baking soda a k a sodium-bicarbonate, and it's carbon dioxide that gives pancakes lift.
Like most people, you probably use double acting baking powder. If so, it probably contains baking soda, cream of tartar and one other ingredient (usually an aluminum salt). The cream of tartar is a dry acid made from wine leas. When the baking powder becomes wet the tartaric acid and baking soda mix in solution and react -- Voila! Bubbles! However, there's not enough acid in the cream of tartar to convert all the baking soda. When the aluminum salt is heated, it turns into an acid, which releases the remaining bubbles. Hence, the turn "double acting," and hence kuan's suggestion to use cold batter.
There are two keys to fluff for most home cooks. First, sift the dry ingredients. Second, do NOT over-beat the batter. Incorporated but still lumpy is your friend. Some people like to allow the batter a chance to rest before baking to relax the glutens for a more tender cake. Since the resting period takes place in the fridge, you'd make kuan happy. But I doubt "tender" is an issue with your pumpkin pancakes. For lift, the sooner you get the cakes on the griddle, the better. If you need more tenderness, switch from AP to cake flour (less gluten).
If you use single acting baking powder (Royal or homemade) you can't let the batter rest at all, you must start baking right away. To make your own single-acting baking powder mix 2 tbs cream of tartar with 1 tbs baking soda and 1 tbs corn starch. Keep absolutely dry, and use within three months. A lot of people prefer this to commercial brands because they taste the aluminum or consider it dangerous. Rumford, a brand you don't see every where, is a double-acting powder without any aluminum. It's good, but not quite as strong as the regular commercial brands like Clabber Girl, Eagle or Calumet.
One disagreement with kuan, chances are you don't want to beat the egg whites separately. It's not a bad idea for airy waffles, but you won't be happy with pancakes made that way. What you'll likely end up with is either a fallen, free-form, half-raw in the center, souffle; or a high-and dry one. Not that it can't be done, it's just problematic.
Hope this helps,