The problem with this is that the cost drivers for seniors tend to be things for which there is no way to trade down. Medications cost what they cost. The consumer has no bargaining power and is bound by the rates set by insurance companies. The same goes for medical care. No one negotiates the cost of a heart by-pass or an emergency appendectomy. There is no "cheaper option".

Rep. Peter DeFazio (D-OR) really thinks the idea of a chained CPI for Social Security is a disastrous one, and does a good job of explaining why? Video if you have poor eye sight. link

...Mr. Furman who work for President Obama say "we're [...] overstating inflation with the way we adjust, so there's something called 'substitution effect,' so when prices of things go up, you buy something cheaper so that means there isn't inflation."

Well, no. Wait a minute. The think you used to buy is more expensive so you're buying something else. In the pointy head economics world this makes sense. So let's see how this would work for someone on Medicare. Okay, you can't afford your heart bypass so instead you'll say to the doctor "look, I can't afford the copay on the heart bypass, why don't you do a hernia instead?" That's substitution, and in Mr. Furman's world this makes sense.

Now what this would do to seniors on Social Security--we already understate inflation, and seniors haven't gotten a COLA for the lat two years. Tell me the price of prescription drugs and medical care hasn't gone up over the last two years. We need, in fact, a different measure for seniors, for Medicare, for veterans for others who consume more health care and more essentials which the CPI doesn't measure. It just measures junk that people buy. That's all it measures. And they're saying because people will buy cheaper junk we should change the CPI.

It would result in reduced in reduced Social Security and veterans benefits.

And then there's this other little impact they're not mentioning. If you're earning $20,000 a year, the tax brackets get adjusted every year. Well, they wouldn't get adjusted so much any more under the chained CPI. So someone who earns $20,000 a year over ten years would see their taxes go up 14 percent. But, guess what? For the rich people, ha. You earn $500,000 a year, you're already at the top, their taxes will only go up 0.3 percent. Three-tenths of one percent. Fourteen percent for someone who earns $20,000 a year. Point three percent for someone who earns $500,000.[...]

Chained CPI: A sneaky plan to cut Social Security and raise taxes

First, the lag present in the final values of chained CPI as well as some of the other data limitations make the implementation of such a policy problematic and would likely make the laws that the policy affects more complicated. Second, the fact that the traditional CPI numbers tend to overstate the true increase in cost of living implies that the chained CPI figures will be lower than the traditional CPI, which means that government benefits that are indexed to inflation will not increase as quickly as they do now, the income cutoffs for tax brackets will not move up as quickly as they do now, and so on. Therefore, adopting chained CPI as the official measure of inflation for these purposes would translate to tax hikes and benefit reductions for a large number of people.

But that latter thing is good, right? We keep hearing about the fiscal cliff and the need to cut the deficit, and it seems like this could be one reasonable way to do so since it would raise taxes and cut spending. While this is true, it's important to consider who would be most affected by this change- given that the most notable program that is indexed to inflation is Social Security, it's likely that such changes will disproportionately impair the elderly. In addition, there is evidence that the tax-bracket changes resulting from adopting chained CPI would disproportionately impact lower-income households. link

NWLC's new analysis finds that for the typical single elderly woman - a woman whose initial benefit is $1,100 per month, the median benefit for single women 65 and older:

• The cut from the chained CPI would reduce her monthly benefits by an amount equal to the cost of one week's worth of food each month at age 80. She would still have two years to wait before receiving any help from the bump-up.

• The Bowles-Simpson bump-up would restore her monthly benefits to current-law levels for only two years - and then her benefits would fall behind again.
  

...
The report also explains that the bump-up would provide no relief to most of the poorest elders who rely on Supplemental Security Income (SSI). SSI beneficiaries would get a double hit from the chained CPI, because it is used to adjust both the initial benefit level and subsequent benefits. But every additional $1 in Social Security benefits reduces SSI benefits by $1 - so a small increase from the bump-up would provide no additional income to most SSI beneficiaries. And some SSI beneficiaries could be even worse off, if the bump-up in their Social Security benefits pushed them slightly above the SSI eligibility threshold - and they lost automatic Medicaid eligibility.

People disabled at an early age also would be severely impacted by the chained CPI. The Bowles-Simpson 20-year bump-up would apply to recipients of disability benefits, starting 20 years after the disability determination. But some proposals for a "birthday bump-up," such as the proposal in the Rivlin-Domenici deficit reduction plan, would provide no help to recipients of disability benefits. link

Now as to your question, which I'm being extremely generous and assuming is meant in good faith.
The answer is, it doesn't matter the size of the group, though I'd recommend it for places with more than 25 people because most of those who hope to commit large massacres will obviously choose concentrations of people as their targets.

From a few reports I've seen (and I know EVERYTHING is still a bit preliminary now) the Principal at Sandy Hook tried to ward off the attacker and gave her life in the process. Perhaps had she had a gun in her office and had been trained to use it, things might have been different.