I said old version are more likely to contains more vulnerabilities.
That doesn't mean that those vulnerabilities will ever be exploited, just that there are more because Nintendo didn't patch them yet.
In case, in the future, one of the old vulnerabilities is exploited, you won't have access to it if it's already patched.
That's why staying on an old version is often recommended.
Look at PS4, a vulnerability was found and exploited on v1.76 while most users were already on v4.x, which means staying on an old firmware is only "in case something happens in the future" which is only gambling and you can never know. Waiting with the old firmware version often means not using the console at all and not playing newer games, etc.. If you want to use it, you should probably update. it has always been a choice by users : wait or update, hack or online, etc.
If you want all the
currently available features, then update to 5.5.1 and you can have Kernel patch and use loadiine and piracy etc.
We don't know yet what will be needed for future exploit (because unreleased) but developers will always try to focus on latest official released firmware first, so you can update and wait.
No IOS developers came and said to stay on an old version, which means they didn't look at the old ones yet, or that old one doesn't have the same vulnerability that they are exploiting.
Is there any game with 5.5.1 update on it? if there are, then there's no hast to update because you will be able to do it later (at a game's price).
If there's no game available to update, and 5.5.1 will be required for any new future hacks, then just hope nintendo doesn't release a new update before the hack is released and before you update your console.
Something nobody ever said about the IOS hack, is whether the hack is independant to the IOS version or not.
is the hack based on a protection which will grant access to all the IOSes, or is the hack focused on a single IOS slot? (wiiu has different slots too, right?)
for example, if the hack is based on "IOS36" and that IOS slot has not been updated since 5.3.0, then you can update or stay where you are, and the hack will work on all versions from 5.3.0 to 5.5.1.
on the contrary, if the hack is not slot specific but more general memory targeted (like MEM2 PROT on wii) and only 5.5.1 can patch it, or if it's specific and the IOS used by the main menu has been updated since your current version, then updates will probably be recommended.
without technical information, it's hard to suggest what to do.
Isn't there a way to spoof updates?
You can spoof the version, but what I think you mean is "is there a way to install updates manually" right?
There's no way to do it, or at least nobody tried because the current WUP installer is done one title at a time, and it would require multiple files updated at the same time. A hardmoded user and a new wup installer would be required to do the tests. but there's a high possibility that system files can't be overwritten without an IOS patch. (like on vWii)
another way to spoof updates is by uing a redirected NAND (emuNAND, redNAND, hardmod NAND backup, etc.), you update the copy instead of the real one.
keeping the old one with vulnerabilities, and updating the copy for latest releases and features.