Sadly, there are more than enough low-life morons willing to 'big-up' their exploits to probably make such endeavours worthwhile. In any event such work would almost certainly be undertaken by civilian employees (that now make up to 50% of some Force's establishments).
Hitherto, such own-goal revelations have only tended to come to light once an investigation's run its course and usually then only by chance. Yes, of course there's issues of identity and intent but that's normally the case in practically every inquiry.
As for the justification on resourcing grounds, that's not always easy or straight forward to quantify. Your average murder enquiry, for example, will invariably require a prodigious investment in time, money and resources, and I mean truly huge. It all depends on the circumstances and it doesn't take much imagination to postulate seemingly unsolvable crimes; script writers do it all the time: random victim, no witnesses, no suspects etc, its seldom easy.
I've been involved in cases where numerous hunches, bogus confessions and plain old red herrings have led to an excess of 5000+ written statements being recorded, not to mention a couple of years hard slog, before good fortune leads to an offender. In such circumstances, every potential lead eventually becomes followed, no matter how tenuous. So an ongoing drip-feed of You-tube etc scrutiny may indeed pay dividends in the long term, though at first thought, it'll probably be about as elusive to quantify as trying to gauge the precise effects of crime prevention. Someone has clearly made a business case for it, I'll be interested to see how it pans out.
Incidentally, I never cease to be amazed that the higher a crime's profile, the more the deranged flock in their droves to 'confess' to it, regardless of consequence.
And with regard to the oft assumed harmlessness of imitation or replica weapons: firearms used in crime are seldom discharged, they don't have to be as the mere threat of use is sufficient. This effectively removes any practical difference between the real and the pretend as numerous successful armed robberies will evidence. Here, its the criminal's intention which is paramount. It gets really tough to deal with when they tell you they have a loaded weapon but you can't see it properly (in cover, darkness, under a coat etc). You really don't want to be stood out in the open when that happens as you very quickly start running out of options; but that's another story.
Furthermore, its not always obvious deciding when someone should be taken seriously or not. An unarmed colleague of mine once stupidly convinced himself that the small gobby 13 year old in the playground only had a toy gun until the little sod suddenly shot him in the cheekbone with a .22 pellet; I think that's called learning the hard way.