Silly bandz as their name implies are silly, and is a fad that will go out with the wind. But while it is here is making a big splash. You made a decision that you felt was right. Kol Hakavod. Another thing one can do, if they feel they can’t just give in and spoil a child is say, “OK, I guess we can buy it but we will just hold on to it till Shabbos or Erev Shabbos as a special Shabbos treat”, which will give it a little meaning. It will also get them accustomed to at least wait a little bit and not get accustomed to instant gratification.
Another way parents can not indulge but allow their children to have the things others have is by earning them, as you said with charts, but since charts might take too long for something as small as silly bands, you can think of something else the parent and the child are working on. For instance, it you are struggling with bed time, or breakfast, or preparing their knapsack for school. If they do 4 or 5 consecutive days they can earn that prize or privilege. In that way you are not just spoiling them with things they want at whim, they are earning things by seriously concentrating on something they need to work on that they might not have necessarily put the effort in before. If the goal of accomplishing the task was not enough to get the job done, maybe the goal of getting the prize or the privilege will help motivate them.
Or they can get the prize for helping Mommy prepare for Shabbos or reading to a sibling or helping a sibling with homework. There are many ways for children to earn a reward or a special treat for doing something special or going above and beyond the call of duty. When my kids were little I used coupons and I had a prize bags with different dollar values. Some had big toys and some had chatchkes. The kids earned coupons of various denominations for various jobs and tasks and would redeem their coupons according to the dollar value and the prize they wanted. If they wanted something right away they would turn the coupons in and get something. If they were saving up for something “big” they waited until they had enough. So basically THEY were in control of what they got.