Sometimes, you have clues to help you make a decision. When I saw the Falcon figure, I instantly knew that I have to wait. First, it costs more than the regular Marvel Universe figure. Second, Falcon is not as popular compared to the other Avengers, specially those that have been featured in the movie. Third, there are relatively more units being sold compared to other characters (Black Widow). And lastly, I had the older version which I turned into another character, so I don't want him that bad. I do like the articulation in the new version. I waited and got 50% discount.
It was almost the same case for Whirlwind. The price is higher. Booo! The character is a villain and not a popular one at that, but I do know the character. He seems like a "good" foe for Wasp and I have been wanting to do a fight scene for Wasp. The reason I bought him right away is because I only found one Whirlwind figure in all 8 toy stores I visited. I have been seeing eBay sellers offering him for a lower price but I find the seller(s) too cocky with their fussy requirements.
Although I consider the supply when deciding to buy right away, experience told me that this is not always a reliable guide. Sometimes, they just display a few. Sometimes, there are more shipments later. This was what happened when I bought Wasp. Since she's a female figure, there was a smaller supply. She was even bundled with other figures (which I didn't want) and buying the set was the only way to get her. Now, there are individual units for Wasp becoming peg warmers. I felt cheated. When I feel cheated, it discourages me to buy in the future.