Clint Dempsey is due to appear on The Late Show With David Letterman on Wednesday night – a symbolic mainstream anointment for a USA team returning from the World Cup to a country that had watched them in their millions.

But when his USA team-mates Kyle Beckerman and Nick Rimando touched down at Atlanta airport on their return, they each had rather more prosaic invites – text messages from their club coach, Real Salt Lake’s Jeff Cassar. Might they be fit to play against New England the next day?

The pair duly played in a 2-1 victory, to revive the fortunes of a team that had slumped in their absence. And it was done in front of a capacity crowd of 20,513, the sixth time in eight home matches Salt Lake have had a full house.

Beckerman and Rimando were not the only ones. Brad Davis’s Houston Dynamo side had not scored in five games after he left for team camp. Davis also started, against New York Red Bulls, and scored a late equalising penalty.

Major League Soccer, which is in mid-season, has been missing a raft of players who may have been far from household names when they left, but who were vital for their domestic teams. The champions, Sporting KC, have been missing Matt Besler and Graham Zusi; Toronto their expensive midfield engine, Michael Bradley. Table-topping Seattle have been without Dempsey, not to mention the wunderkind DeAndre Yedlin. On Sunday the pair will return to club action against Portland Timbers in front of an expected crowd of 67,000. The team average more than 40,000 fans for every league match.

Only four MLS players made the squad for South Africa 2010 but when the USA lined up to face Germany last month, there were seven in the starting lineup.

Some of this is down to a reverse migration that started last summer with the return of Dempsey from Tottenham, and became a mini-flood before the start of the 2014 MLS season in March – with Bradley one of a number of players who traded in a European clubs for well-remunerated MLS deals in a World Cup year.

Jürgen Klinsmann, who had once warned Dempsey that he “hadn’t done shit” just because he had got a contract at Spurs, was as publicly unimpressed at what appeared to be mass regression as his dual role as USA coach and technical director for US Soccer (including MLS) would allow.

But Klinsmann had already shown that he was willing to promote MLS players to the first team as long as he felt they were striving to reach a benchmark of international standards. Until just before the World Cup, his starting centre-back pairing of Besler and LA Galaxy’s Omar Gonzalez were typical of that tendency.

Klinsmann, with his longer-term vision for the 2018 team, would probably concede that for all its historic faults, some of which persist, the MLS will be the cornerstone of meaningful technical advancement in the US, if it is to happen at all. A rinse-and-repeat four-year cycle of finding talented US players wherever they happen to be around the world will not take the country any further than it has already gone.

For the league, which has expanded the number of clubs rapidly, and by extension transformed its ownership culture in recent years, the return of the US players is part of a strategy that has started to shift from a focus on dedicated stadiums and infrastructure, towards technical development.

But it is another more immediate return that is under scrutiny this week. World Cups traditionally represent a high watermark in attention for the sport everywhere in the world, and the US has been no different. But its recent highs have been dramatic: ESPN’s TV figures for the World Cup are 44% up on 2010, and 122% up on 2006.

Furthermore, ESPN, Fox and Univision all collaborated on an eight-year deal with the league and US Soccer just before the tournament that will also give the MLS a regular TV time slot it has not historically had. Since 2010 MLS average attendances have climbed 11% to 18,503. The question now is that with a critical mass of players returning from the World Cup with increased recognition, can such numbers translate into interest in and revenue for the domestic league?

Just as crucially, can it do so in a way that sees the league become, as the writer Will Kuhns recently put it, a true “crucible” for talent to be forged and tested? Executives, investors and coaches will be watching the coming months closely, long after Letterman’s last guest has left the building.