Personally, I find it hard to believe that Stalin (and the nomenklatura in general that has been enabling him) would just see the error of his ways because of the UASR. On the surface, it would be fine, with state visits, speeches about the virtues of communist internationalism, cultural and scientific exchanges and so on, but the history of the UASR-USSR relations between the Revolution and the WW2 will read like a thriller. When dealing with the allies, Stalin was too astute a diplomat to let the USSR be sidelined.
For starters, I think that it would control its image abroad even more than id dit OTL. Both the Americans coming to the USSR and Soviet citizens going to the UASR will be thorougly vetted. For every American visitor able to see what the Soviet regime has become and shout about it from the roofs, there will be five dyed in the wool Stalinists, four cynics who see what happens but think that it's better to do what's expedient than what's right, and eighty dupes content to be drip-fed by Stalinist propaganda and orchestrated field trips (think Walter Duranty).
The image of the American revolution formed by the Soviet media for the internal consumption will be rather interesting, too - features most close to the Soviet ones will be lionized, the rest will be deliberately misinterpreted to look exactly the same as their Soviet counterparts, explained as something transitional on the way to Communism, or pointedly ignored.
As a side note concerning the numerous Soviet delegations in America, I'd expect that a sizeable part of them will be the GRU and GUGB operatives working undercover - to keep the rest in line, to plant agents of influence, and to do whatever ordinary spies are doing (even if the UASR keeps no secrets from the Soviet 'elder sister', Stalin will never believe it).
In the Comintern, Stalin has lost the majority, but that doesn't mean he would quietly accept that. I see at least two ways for the Soviets to regain the majority: campaigning against the individual parties' reunion with the factions that have split earlier (as it has already happened to the Communist party of Spain) and supporting the creation of communist parties in the colonies (something that happened IOTL, but here, it will be done to a greater extent), in the hopes that their leadership will be pro-Soviet rather than pro-American.