When people start stating credentials, you know the thread is heading nowhere good, though this one seems to have recovered. I just want to point out, parenthetically, that in an anonymous forum, saying "I prefer X", is not substantively different than saying, "As a Nobel Prize winning engineer with 100 years of experience working with X and Y, I prefer X." The credentials clause is just about ego or trying to establish credibility. The problem with credibility is that, the reader needs to believe you in the first place or the credentials argument is voided. That just leaves ego, and I say this as a person with a PhD in psychology and having spent the last 100 years studying this phenomenon ... and I invented the internet.
My response to Ajay's original post:
Most people (obviously at this point) agree that replacing the bracket is a good idea. The practical part of this advice is that, at least anecdotally, the SS bracket is less prone to failure, or at least failure without warning. I don't personally have any experience with anyone who has had this happen, so I don't know how much of this risk is theoretical and how much is statistical. (I recently had a bunch of people swearing that I would spontaneously lose my keel if I didn't sister the old keel bolts, though no one could produce an example of this having ever happened.)
But, I do know this:
Sailors do a lot of worrying about theoretical risks. That is, they tend to err on the side of caution and devote quite a bit of time and money addressing things that are, in actuality, only theoretically a risk, even when there is no evidence that the problem has ever occurred. There are good reasons for that caution, but it must be tempered with reason.
Now, spreaders and spreader brackets DO fail, and the risk of demasting at that point is not simply theoretical. Do THESE brackets fail? Well, according to a few sources (those who sell the upgrades), they do. I would ask the forum at this point, "Who here has any knowledge, direct or otherwise, of anyone who has had this happen?"
I honestly don't know. It could be that it happens all the time. I've just never heard of it ACTUALLY happening.
With that said, to me, it's not worth the risk. The new brackets are, what, $100 - $150? I personally wouldn't bring the mast down just to make this change, but if the mast was down for any reason, I would replace them. This is just a peace-of-mind issue for me, having some knowledge of how aluminum fails vs steel.
And with that said, as has been mentioned, you can't really say much summarily about either aluminum or SS. There is so much variation, in particular because many materials are called "aluminum" which are actually alloys. I don't know enough about either material, or the actual quantified forces involved at the spreader bracket, to make an informed decision about which grades of either aluminum or SS are suitable.
Unfortunately, neither does anyone here, despite stated credentials to the contrary. In terms of engineering, the problem is VERY complex and cannot be summed up with knowledge of the specs of the relevant materials.
A good friend of mine is a pipe engineer (yes, there really is such a thing). We were discussing bike frames (actually the relative merits of aluminum vs steel). He explained to me that the problem was so complex that you could do a dissertation on just one joint in the bike, and still get it wrong when it comes to what actually happens. Early aluminum bike frames DID crack and fail without warning. This is not because the engineers were inept, but because they lacked empirical data about what would actually happen in the real world. Aluminum frames have been around a while now, and they no longer have this problem, demonstrating that it is not the material, it is the knowledge of applying the material appropriately, informed by the actual stresses involved and the material's responses to those stresses.
This brings me back to my earlier point that, before saying that the "upgrade" is better, I'd like to know empirically that the aluminum one fails more frequently (under comparable conditions) than the SS one. I don't think anyone can make the claim to have reliable data for this. So, it just leaves us with the peace-of-mind factor.
But, I will say this. The cast aluminum bracket was likely produced merely with economy in mind. The SS bracket is produced, at least apparently, with materials that have been proven in similar applications. I don't think that we even actually know what materials the aluminum brackets were produced with. (Does anyone here know this?)
So, all I think that we can say that the SS brackets are probably reliable, and that there is less of a chance that the aluminum brackets are as reliable. But, I don't think we can say (at least not with the information I am aware of) that either is inadequate.