You don't need troops close to a first-world level for peacekeeping - light infantry, equipped to about the level of modern NZ troops, is fine.
But lets pull this into an example where UN peacekeepers might have been handy, with an event that probably would have rolled along regardless of OTL changes.
In 1974, Portugal's long-term military dictatatorship fell. This led to the independance war in Angola being decided in favour of the rebels - but which rebels ? You have MLPA, FNLA and UNITA and the Cabinda secessionists, all of whom had regional and/or superpower backers.
Now, if the UN picks a side in the 1975 civil war and sends troops in - and remember, we're dealing with a 'more effective at peacekeeping UN', which means their peacekeepers (from Fiji, Sweden or wherever) need to be prepared to shoot at Cuban, South African, CIA and even Soviet 'advisors' - what happens ?